T cell responses and viral escape

OBJECTIVE: Median sternotomy was performed by 2 different techniques in order to determine whether there was a difference in the incidence of inadvertent pleural entry. EXPERIMENTAL DESIGN: Patients were prospectively evaluated and reviewed at a mean follow-up interval of 8.2 months. PATIENTS AND METHODS: Ninety five consecutive patients underwent primary sternotomy at a single tertiary referral center. MEASURES: Planned outcome measures included, incidence of pleural entry, length of hospitalization, and chest tube site related postoperative morbidity. RESULTS: Group 1 (n=49) had sternotomy undertaken from the sternal notch proceeding downwards. Group 2 (n=46) underwent sternotomy performed from the xiphoid upwards. Mediastinal evaluation revealed a significant reduction in the incidence of pleural violation for group 1 (3) versus group 2 (11) (p=0.014). This difference was not found to be surgeon specific. CONCLUSIONS: Sternotomy undertaken from the sternal notch proceeding downwards is shown to be associated with a reduced incidence of inadvertent pleural entry. Potential advantages for this approach also include reduced respiratory morbidity, less chest tube site complications and a trend to reduced length of hospitalization.     

Anergic T cells actively suppress T cell responses via the antigen-presenting cell

We here show that anergic T cells are active mediators of T cell suppression. In co-culture experiments, we found that anergic T cells, derived from established rat T cell clones and rendered anergic via T cell presentation of the specific antigen (Ag), were active inhibitors of T cell responses. Anergic T cells inhibited not only the responses of T cells with the same Ag specificity as the anergic T cells, but were also capable of efficiently inhibiting polyclonal T cell responses directed to other epitopes. This suppression required close cell-cell contact between antigen-presenting cells (APC), anergic T cells and responder T cells, and only occurred when the epitope recognized by the anergic T cell was present. The suppression was not caused by passive competition for ligands on the APC surface, IL-2 consumption, or cytolysis, and was not mediated by soluble factors derived from anergic T cells that were stimulated with their specific Ag. When responder T cells were added 24 h after co-culturing anergic cells in the presence of Ag and APC, T cell responses were still suppressed, indicating that the suppressive effect was persistently present. However, anergic T cells were not able to suppress responder T cells that had already received a full activation signal. We propose that suppression by anergic T cells is mediated via the APC, either through modulation of the T cell-activating capacity of the APC (APC/T cell interaction), or by inhibition of T cells recognizing their ligand in close proximity on the same APC (T/T cell interaction).     

Vigorous HIV-1-specific CD4+ T cell responses associated with control of viremia

Virus-specific CD4+ T helper lymphocytes are critical to the maintenance of effective immunity in a number of chronic viral infections, but are characteristically undetectable in chronic human immunodeficiency virus-type 1 (HIV-1) infection. In individuals who control viremia in the absence of antiviral therapy, polyclonal, persistent, and vigorous HIV-1-specific CD4+ T cell proliferative responses were present, resulting in the elaboration of interferon-gamma and antiviral beta chemokines. In persons with chronic infection, HIV-1-specific proliferative responses to p24 were inversely related to viral load. Strong HIV-1-specific proliferative responses were also detected following treatment of acutely infected persons with potent antiviral therapy. The HIV-1-specific helper cells are likely to be important in immunotherapeutic interventions and vaccine development.     

Human eosinophils produce biologically active IL-12: implications for control of T cell responses

The present study assessed the capacity of eosinophils (EOS) to synthesize the cytokine IL-12. Blood-derived, highly purified human EOS from six atopic patients and two nonatopic individuals were treated in culture with IL-4, IL-5, granulocyte-macrophage CSF, IFN-gamma, TNF-alpha, IL-1alpha, RANTES, and complement 5a, respectively. The expression of both IL-12 protein and mRNAs for the p35 and p40 IL-12 subunits was strongly induced in all donors by the Th2-like cytokines IL-4 and granulocyte-macrophage CSF and was also moderately induced by TNF-alpha and IL-1alpha. IL-5 treatment resulted in IL-12 synthesis in four atopic donors and one nonatopic donor, whereas IFN-gamma induced IL-12 synthesis in only two atopic donors. In contrast, RANTES exclusively induced mRNA for the p40 subunit without detectable protein release, and complement 5a had no effect on IL-12 mRNA or protein expression. EOS-derived IL-12 was biologically active, because supernatants derived from IL-4-treated EOS superinduced the Con A-induced expression of IFN-gamma by a human Th1-like T cell line. This activity was neutralized by anti-IL-12 Abs. In conclusion, EOS secrete biologically active IL-12 after treatment with selected cytokines, which mainly represent the Th2-like type. Consequently, EOS may promote a switch from Th2-like to Th1-like immune responses in atopic and parasitic diseases.     

Bovine T cell responses to Cryptosporidium parvum infection

To better understand the immune mechanisms important for clearing of the primary infection and the subsequent development of resistance to Cryptosporidium parvum infection, several groups have recently characterised changes within the lymphoid cell population of the intestinal mucosa and associated lymphoid tissue in calves with cryptosporidiosis. In naive animals, infection results in a significant increase in the number of CD4+ and CD8+ T cells present within the intraepithelial lymphocyte population, lamina propria and Peyer's patch of the ileum. This is accompanied by a rapid and transient increase in the number of gamma/delta T cells present within the intestinal villi. In response to a challenge infection in immune calves, there is a substantial increase in the number of CD4+ T cells present in the Peyer's patch of the ileum and a specific localization of CD8+ T cells to the epithelium of the intestinal villi. Together, these data demonstrate that C, parvum elicits a strong cell-mediated response following both primary and secondary infections in calves, and that CD8+ T cells may play an important role in the bovine immune response to C. parvum infection.     

Leishmania donovani infection initiates T cell-independent chemokine responses, which are subsequently amplified in a T cell-dependent manner

Control of Leishmania donovani infection in immunocompetent mice is associated with hepatic inflammation and granuloma formation, both of which are absent in severe combined immunodeficient (scid) mice. In both BALB/c and scid mice, L. donovani infection induced a rapid hepatic accumulation of mRNA encoding macrophage inflammatory protein-1alpha (MIP-(1alpha), monocyte chemoattractant protein-1 (MCP-1) and interferon-gamma inducible protein-10 (gammaIP-10). This response was not preceded by increased IL-4 production in either strain, unlike that reported in other infectious disease models. Interestingly, only gammaIP-10 mRNA was maintained at elevated levels throughout the first 7 days of infection, by mechanisms involving CD4+ and CD8+ T cells, and CD4+CD8+ cells not activated in scid mice. By in vivo depletion and reconstitution of scid mice it was demonstrated that T cells regulate the expression of all three chemokines studied, while they themselves only produce gammaIP-10 in appreciable quantities.     

The nature of the signals regulating CD8 T cell proliferative responses to CD8alpha+ or CD8alpha- dendritic cells

The CD8alpha(-)-expressing dendritic cells (DC) of mouse spleen have been shown to be poor inducers of interleukin (IL)-2 production by CD8 T cells when compared to the CD8- DC. As a consequence, CD8 T cells give a more prolonged proliferative response to CD8- DC than to CD8+ DC. The possible mechanisms underlying these functional differences in DC subtype have been investigated. Inadequate co-stimulation did not underlie the poor T cell response to allogeneic CD8+ DC. Equivalent levels of B7-1 (CD80) and B7-2 (CD86) were found on the two DC subtypes and co-stimulator assays did not reveal any functional differences between them. Although CD8+ DC were found to die more rapidly in culture than CD8- DC, this did not explain their reduced stimulatory ability. Neither prolonging DC survival in culture nor renewing the stimulator cells by repeated addition of freshly isolated DC had any significant effect on the T cell responses. Furthermore, later addition to the cultures of DC of the opposite type to the initiating DC did not reverse or eliminate the differential response to the initiating DC. The role of DC-derived soluble factors was examined by addition to the cultures of supernatants derived from freshly isolated or stimulated DC of the opposite type. This neither enhanced the poor stimulatory capacity of CD8+ DC nor inhibited the stimulation by CD8- DC. Furthermore, addition of a series of cytokines that might have been produced by the DC did not eliminate the differences in T cell proliferation. Only the addition to the cultures of the growth factors IL-2 and IL-4 overcame the stimulatory difference between the two DC populations, confirming that the difference in T cell proliferative responses was a consequence of differences in induced cytokine production. The difference in the response of CD8 T cells to CD8+ and CD8- DC is therefore determined by direct DC-T cell contact during the earliest stages of the culture and involves an undetermined and possibly new signaling system.     

Two separable T cell receptor signals reconstitute positive selection of CD4 lineage T cells in vivo

Positive selection is an obligatory step during intrathymic T cell differentiation. It is associated with rescue of short-lived, self major histocompatibility complex (MHC)-restricted thymocytes from programmed cell death, CD4/CD8 T cell lineage commitment, and induction of lineage-specific differentiation programs. T cell receptor (TCR) signaling during positive selection can be closely mimicked by targeting TCR on immature thymocytes to cortical epithelial cells in situ via hybrid antibodies. We show that selection of CD4 T cell lineage cells in mice deficient for MHC class I and MHC class II expression can be reconstituted in vivo by two separable T cell receptor signaling steps, whereas a single TCR signal leads only to induction of short-lived CD4+CD8lo intermediates. These intermediates remain susceptible to a second TCR signal for 12-48 h providing an estimate for the duration of positive selection in situ. While both TCR signals induce differentiation steps, only the second one confers long-term survival on immature thymocytes. In further support of the two-step model of positive selection we provide evidence that CD4 T cell lineage cells rescued by a single hybrid antibody pulse in MHC class II-deficient mice are pre-selected by MHC class I.     

T cell responses to heat-shock protein 60: differential responses by CD4+ T cell subsets according to their expression of CD45 isotypes

We demonstrate that human T lymphocytes proliferate in vitro to highly purified human heat-shock protein 60 (Hu.hsp60). The response to this self Ag was confined to the CD45RA+ RO- T cell subset, with minimal responses by adult CD45RA- RO+ T cells. Experiments using keyhole limpet hemocyanin as a prototypic novel Ag, or tetanus toxoid as a recall Ag, were consistent with the notion that CD45RA+ RO- and CD45RA- RO+ T cell subsets can be designated as naive and memory cells, respectively; thus, responses to Hu.hsp60 were confined to the putative naive subset. In contrast, both CD45RA+ RO- and CD45RA- RO+ T cell populations proliferated to bacterial hsp60 from Mycobacterium leprae, Escherichia coli, or Chlamydia trachomatis. However, only CD45RA- RO+ (memory) T cells responded to a mycobacterial hsp60-derived peptide previously defined as a major bacteria-specific epitope. Experiments with cord blood T cells, which are CD45RA+ RO- and can be considered truly naive, showed that the peptide could elicit responses from naive T cells in vitro; cord blood cells also responded to Hu.hsp60. Since bacterial hsp60 Ags contain both conserved and nonconserved epitopes, we speculate that in vivo challenge with bacterial hsp60 will activate T cells capable of seeing either type of epitope, but only those that see nonconserved epitopes maintain the CD45RA- RO+ memory phenotype. However, T cells recognizing conserved epitopes, while not apparently being recruited to the memory pool, may nevertheless play a role in immunoregulation, particularly in the context of inflammation, when expression of Hu.hsp60 is increased.     

T cell responses to natural human proteins in primary biliary cirrhosis

The study of T cell responses to autoantigens in human autoimmunity has been hampered by difficulties, firstly in identifying significant autoantigens, and secondly in the purification of authentic human proteins in sufficient quantities to allow characterization of antigen-specific T cell responses. In this study we have purified a human autoantigen, pyruvate dehydrogenase, retaining its enzymatic activity, and characterized autoreactive T cell responses to it in a human autoimmune disease, primary biliary cirrhosis. T cell responses to a mixture of the E2 and protein X subunits of human pyruvate dehydrogenase complex are seen in most affected patients, but in only a small minority of normal and chronic liver disease controls. By contrast, responses to whole pyruvate dehydrogenase complex occur with equal frequency in both groups. This suggests that responses to the E2 component/protein X of pyruvate dehydrogenase complex play a role in the pathogenesis of primary biliary cirrhosis. The availability of significant quantities of the human autoantigen in primary biliary cirrhosis makes this condition an interesting model in which to study true autoreactive human T cell responses.     

Integrating cytosolic calcium signals into mitochondrial metabolic responses

Stimulation of hepatocytes with vasopressin evokes increases in cytosolic free Ca2+ ([Ca2+]c) that are relayed into the mitochondria, where the resulting mitochondrial Ca2+ ([Ca2+]m) increase regulates intramitochondrial Ca2+-sensitive targets. To understand how mitochondria integrate the [Ca2+]c signals into a final metabolic response, we stimulated hepatocytes with high vasopressin doses that generate a sustained increase in [Ca2+]c. This elicited a synchronous, single spike of [Ca2+]m and consequent NAD(P)H formation, which could be related to changes in the activity state of pyruvate dehydrogenase (PDH) measured in parallel. The vasopressin-induced [Ca2+]m spike evoked a transient increase in NAD(P)H that persisted longer than the [Ca2+]m increase. In contrast, PDH activity increased biphasically, with an initial rapid phase accompanying the rise in [Ca2+]m, followed by a sustained secondary activation phase associated with a decline in cellular ATP. The decline of NAD(P)H in the face of elevated PDH activity occurred as a result of respiratory chain activation, which was also manifest in a calcium-dependent increase in the membrane potential and pH gradient components of the proton motive force (PMF). This is the first direct demonstration that Ca2+-mobilizing hormones increase the PMF in intact cells. Thus, Ca2+ plays an important role in signal transduction from cytosol to mitochondria, with a single [Ca2+]m spike evoking a complex series of changes to activate mitochondrial oxidative metabolism.     

Single-cell cytokine analysis of gamma delta T cell responses to nonpeptide mycobacterial antigens

TCR gamma delta T cells are considered important in the rapid immune response to intracellular infection. We investigated the early response of peripheral blood gamma delta T cells to the nonpeptide Ag isopentenyl pyrophosphate and to its synthetic analogue ethyl pyrophosphate. In healthy donors, an increase in the number of gamma delta T cells was detected as soon as 4 days after stimulation with the nonpeptide Ags. Single-cell analysis of cytokine production was performed by intracellular staining of IFN-gamma and IL-4. gamma delta T cells were found to rapidly expand and produce IFN-gamma in response to nonpeptide Ags. Furthermore, IL-12 augmented the IFN-gamma response. In contrast, gamma delta T cells from the majority of HIV+ donors did not expand or express IFN-gamma in response to nonpeptide Ags, even in the presence of IL-12. These findings indicate a role for nonpeptide-reactive gamma delta T cells in effective cell-mediated immunity for intracellular pathogens.     

T cell cytokine responses in persons with tuberculosis and human immunodeficiency virus infection

Tuberculosis causes more extensive and life-threatening disease in patients with HIV infection than in immunocompetent persons. To investigate the hypothesis that these severe manifestations of tuberculosis may be due to alterations in cytokine production, we evaluated cytokine patterns in HIV-infected tuberculosis patients. Upon stimulation with Mycobacterium tuberculosis in vitro, PBMC from HIV-infected tuberculosis patients had reduced proliferative and type 1 responses, compared with HIV-seronegative tuberculosis patients. The reduction in proliferative responses was independent of the CD4 cell count, but the reduced type 1 response was a direct result of CD4 cell depletion. There was no enhancement of type 2 cytokine production in HIV-infected patients, although production of IL-10 was prominent in all tuberculosis patients. In HIV-infected tuberculosis patients, M. tuberculosis-induced proliferative responses were significantly enhanced by neutralizing antibodies to IL-10 but not by antibodies to IL-4 or by recombinant IL-12. The M. tuberculosis-induced type 1 response was augmented both by antibodies to IL-10 and by recombinant IL-12. Tuberculosis in the context of HIV infection is characterized by diminished type 1 responses, probably induced by immunosuppressive cytokines produced by macrophages/monocytes, rather than by type 2 cells.     

IL-6 produced by macrophages infected with Mycobacterium species suppresses T cell responses

The ability of Mycobacterium bovis Calmette-Guérin bacillus-infected bone marrow-derived macrophages to process and present exogenously added Ags to T cells and stimulate their growth and production of IL-2 was examined. The infected macrophages were inhibited in their ability to activate T cells, and this inhibition could be transferred to uninfected macrophages with filtered supernatants from mycobacteria-infected macrophages. The inhibition was not due to decreases in macrophage viability, Ag uptake, or cell surface expression of MHC class II or other accessory molecules necessary for Ag presentation. Other intracellular pathogens such as Listeria monocytogenes and Leishmania mexicana did not induce the soluble inhibitory factor, while Mycobacterium avium strain 101 did, suggesting the factor is specific to infection with mycobacteria. The inhibitory effect was reversed completely by preincubation with neutralizing Abs against IL-6, and rIL-6 partially restored the effect. Approximately 10,000-fold more IL-6 was produced by mycobacteria-infected macrophages compared with uninfected controls. Such sustained levels of IL-6 may account for the immune unresponsiveness apparent in both human and murine mycobacterial disease.     

A peptide binding weakly to the major histocompatibility molecule augments T cell responses

An I-A(d)-derived peptide PB1 was found to enhance the reactivity of I-A(d)-restricted T cells. The augmentative effect was not due to the cross-reactivity of PB1 peptide with antigens. PB1 had no effect on T cells specific for I-A(b) and I-E(k), nor did PB1 increase the T cell responses to concanavalin A and staphylococcal enterotoxin B. The strict I-A(d) specificity suggests that PB1 enhances the recognition of antigen-I-A(d) complex by T cell receptor. PB1 bound to I-A(d) weakly. The augmentative effect could be found on other I-A(d)-binding peptides in appropriate conditions; however, PB1 was distinct in its prominently augmentative effect on all the I-A(d)-restricted T cells analyzed. A similar enhancing activity was demonstrated on a synthetic transferrin receptor peptide with minimum affinity for I-A(d). The unusual enhancing activity of PB1 may thus be attributed to the low I-A(d) binding affinity. It was postulated that the binding of low-affinity PB1 would not only stabilize I-A(d) structure, but also enhance the binding of other peptides. This was supported by the increased binding of OVA 323-339 and cI 84-98 to I-A(d) in the presence of PB1. The inclusion of PB1 in the immunization mixture also enhanced T cell responses in vivo, suggesting the possibility of using low-affinity peptide to promote specific immunity.     

Secondary but not primary T cell responses are enhanced in CTLA-4-deficient CD8+ T cells

Negative as well as positive co-stimulation appears to play an important role in controlling T cell activation. CTLA-4 has been proposed to negatively regulate T cell responses. CTLA-4-deficient mice develop a lymphoproliferative disorder, initiated by the activation and expansion of CD4+ T cells. To assess the function of CTLA-4 on CD8+ T cells, CTLA-4(-/-) animals were crossed to an MHC class I-restricted 2C TCR transgenic mouse line. We demonstrate that although the primary T cell responses were similar, the CTLA-4-deficient 2C TCR+ CD8+ T cells displayed a greater proliferative response upon secondary stimulation than the 2C TCR+ CD8+ T cells from CTLA-4 wild-type mice. These results suggest that CTLA-4 regulates antigen-specific memory CD8+ T cell responses.     

Resting respiratory tract dendritic cells preferentially stimulate T helper cell type 2 (Th2) responses and require obligatory cytokine signals for induction of Th1 immunity

Consistent with their role in host defense, mature dendritic cells (DCs) from central lymphoid organs preferentially prime for T helper cell type 1 (Th1)-polarized immunity. However, the "default" T helper response at mucosal surfaces demonstrates Th2 polarity, which is reflected in the cytokine profiles of activated T cells from mucosal lymph nodes. This study on rat respiratory tract DCs (RTDCs) provides an explanation for this paradox. We demonstrate that freshly isolated RTDCs are functionally immature as defined in vitro, being surface major histocompatibility complex (MHC) II lo, endocytosishi, and mixed lymphocyte reactionlo, and these cells produce mRNA encoding interleukin (IL)-10. After ovalbumin (OVA)-pulsing and adoptive transfer, freshly isolated RTDCs preferentially stimulated Th2-dependent OVA-specific immunoglobulin (Ig)G1 responses, and antigen-stimulated splenocytes from recipient animals produced IL-4 in vitro. However, preculture with granulocyte/macrophage colony stimulating factor increased their in vivo IgG priming capacity by 2-3 logs, inducing production of both Th1- and Th2-dependent IgG subclasses and high levels of IFN-gamma by antigen-stimulated splenocytes. Associated phenotypic changes included upregulation of surface MHC II and B7 expression and IL-12 p35 mRNA, and downregulation of endocytosis, MHC II processing- associated genes, and IL-10 mRNA expression. Full expression of IL-12 p40 required additional signals, such as tumor necrosis factor alpha or CD40 ligand. These results suggest that the observed Th2 polarity of the resting mucosal immune system may be an inherent property of the resident DC population, and furthermore that mobilization of Th1 immunity relies absolutely on the provision of appropriate microenvironmental costimuli.     

CD4+ alpha beta T cell and gamma delta T cell responses to BCG in patients with pulmonary tuberculosis--comparison with healthy controls

PURPOSE: We evaluated retrospectively the socioeconomic development of epilepsy patients after temporal or extratemporal epilepsy surgery and analyzed the relationship to clinical and neuropsychological data. METHODS: 151 patients (from ages 11-65 years; mean postoperative followup: 3 years) replied to a structured questionnaire, which referred to objective data of the patient's educational and vocational development. Neuropsychological data were obtained from pre- and postoperative (1-year follow-up) examinations. RESULTS: The preoperative development data indicated that patients exposed to epilepsy at any developmental stage had a higher prevalence of educational/vocational difficulties as compared with patients with a later onset of epilepsy. Postoperatively, the integration of the formerly unemployed improved and the unemployment rate decreased from 33 to 16%. Out of those patients who had been schooled or who were employed, 79%-91% made progress in development, or were at least able to keep their status. Only 2 of 14 patients, who had been retired early because of their epilepsy, returned to employment. In general, a deterioration of the socioeconomic status was significantly related to insufficient seizure control. A reemployment of patients who were formerly unemployed depended mainly on age and neuropsychological outcome. CONCLUSIONS: Our results suggest that early and successful surgical intervention improves or at least maintains the socioeconomic situation, especially the employment status.     

A case of rapidly progressive T cell type malignant lymphoma which started with multiple cranial neuropathy

A 35-year-old man had suffered from recurrent right trigeminal nerve palsy and flaccid paraparesis for about five months. Cerebrospinal fluid (CSF) showed a marked increase of protein (400 mg/dl) and mononuclear cells (146/mm3), but there were no malignant cells. Antibiotic therapy remitted his inguinal and mediastinal lymph nodes swelling, and trigeminal nerve palsy had recovered spontaneously. Then he developed left trigeminal and facial nerve palsy, mononeuropathy multiplex, and cauda equina syndrome. Nerve conduction studies revealed delayed velocity and reduction of amplitude. Enhanced magnetic resonance imaging showed increased signal intensity in bilateral trigeminal nerves, left internal auditory meatus, and meninges of the basal cistern. Also, there were two mass lesions in cauda equina. They were operated by orthopedist, and were not malignant. After that, CSF cells of malignant lymphoma were elevated and revealed T cell type (large cell). Then the patient exacerbated in bulbar palsy and died. When there is lymph node swelling with multiple neurological deficits, despite remission of lesions and signs, biopsies should be positively pursued early in the patient's clinical course.     

Biophysical signals underlying myogenic responses in rat interlobular artery

-To assess cellular mechanisms mediating myogenic responses of interlobular artery (ILA), experiments were performed with the use of isolated perfused hydronephrotic kidneys. ILAs were divided into 3 groups according to their basal diameters: proximal (>60 microm), intermediate (40 to 60 microm), and distal (<40 microm) ILAs. Myogenic responses were obtained by stepwise increase in perfusion pressure. Greater myogenic responsiveness was observed in ILAs with smaller diameters. Diltiazem (10 micromol/L) inhibited myogenic responses of all segments of ILAs. Furthermore, gadolinium (10 micromol/L), a mechanosensitive cation channel blocker, abolished myogenic responses of distal but not proximal ILA. In contrast, 2-nitro-4-carboxyphenyl-N, N-diphenyl-carbamate (200 micromol/L), an inhibitor of phospholipase C, prevented myogenic responses of proximal but not distal ILA. Finally, basal proximal ILA diameters were increased by treatment with 50 nmol/L of staurosporine (P<0.05), and subsequent addition of thapsigargin (1 micromol/L) blocked myogenic contraction of proximal ILAs. Myogenic responses of intermediate ILAs exhibited characteristics between those of distal and proximal ILAs. Our data indicate that underlying mechanisms for myogenic responses differ in distinct segments of ILAs. The present results suggest that mechanosensitive cation channels are involved in myogenic constriction of distal ILAs. Finally, our findings provide evidence that the stimulation of phospholipase C mediates myogenic contraction of proximal ILAs.