Identification of an IL-7-associated pre-pro-B cell growth-stimulating factor (PPBSF). I. Production of the non-IL-7 component by bone marrow stromal cells from IL-7 gene-deleted mice

Mouse bone marrow (BM) stromal cell conditioned medium (CM) from our long-term lymphoid culture system selectively induces the in vitro proliferation and presumptive differentiation of pre-pro-B cells (B220+, HSA-, TdT- or TdT+, c[mu-]) from adult rat, mouse, and human BM. However, the responsible growth factor(s) has not yet been identified. Inasmuch as IL-7 is one of the cytokines most closely associated with early B-lineage development, we utilized BM adherent cells and stromal cell lines from IL-7 gene-deleted (-/-) mice in combination with rIL-7 and anti-IL-7 mAb to investigate its possible regulatory role in our culture system. The results show that, although rIL-7 and IL-7 (-/-) CM each can maintain the viability of freshly harvested pre-pro-B cells in vitro, neither induces them to proliferate and/or differentiate, even in the presence of recombinant stem cell factor (rSCF) and/or recombinant insulin-like growth factor (rIGF). The results also show that anti-IL-7 mAb fails to neutralize the pre-pro-B cell growth-stimulating activity in IL-7 (+/+) CM. Yet rIL-7 enables IL-7 (-/-) CM to induce proliferation of pre-pro-B cells, and to "prime" them to respond directly to monomeric IL-7. Furthermore, anti-IL-7 mAb adsorbs the pre-pro-B cell growth-stimulating activity from both IL-7 (+/+) CM and rIL-7-supplemented IL-7 (-/-) CM; but rIL-7 does not restore this activity. Lastly, both pre-pro-B cell growth-stimulatory activity and IL-7 are quantitatively recovered by ultrafiltration in the 50 to 100 kDa, rather than the 10 to 50 kDa, apparent molecular mass fraction. These results suggest that the pre-pro-B cell growth-stimulating activity in our culture system is the property of a self-associating complex of IL-7 and a second BM stromal cell-derived cofactor.     

Optimal bit allocation and best-basis selection for wavelet packetsand TSVQ

To use wavelet packets for lossy data compression, the following issues must be addressed: quantization of the wavelet subbands, allocation of bits to each subband, and best-basis selection. We present an algorithm for wavelet packets that systematically identifies all bit allocations/best-basis selections on the lower convex hull of the rate-distortion curve. We demonstrate the algorithm on tree-structured vector quantizers used to code image subbands from the wavelet packet decomposition.     

Embedded multilevel error diffusion

We present an algorithm for image browsing systems that embeds the output of binary Floyd-Steinberg (1975) error diffusion, or a low bit-depth gray-scale or color error diffused image into higher bit-depth gray-scale or color error diffused images. The benefits of this algorithm are that a low bit-depth halftoned image can be directly obtained from a higher bit-depth halftone for printing or progressive transmission simply by masking one or more bits off of the higher bit-depth image. The embedding can be done in any bits of the output, although the most significant or the least significant bits are most convenient. Due to constraints on the palette introduced by embedding, the image quality for the higher bit-depth halftone may be reduced. To preserve the image quality, we present algorithms for color palette organization, or binary index assignment, to be used as a preprocessing step to the embedding algorithm.     

Recent thymic emigrants in the rat express a unique antigenic phenotype and undergo post-thymic maturation in peripheral lymphoid tissues

Studies of the functional properties and developmental potentials of immediate post-thymic cells have been hampered by the lack of reliable markers with which to distinguish recent thymic emigrants (RTE) from the bulk of peripheral T cells. In the present study, the intrathymic FITC-labeling technique was used in concert with three-color flow-cytometric analysis to identify, phenotypically characterize, and study the short term fate of RTE in normal rats. The results indicated that between 3 and 4% of total T cells in lymph node and spleen of 5- to 8-wk-old rats had been released from the thymus within the preceding 24 h. Unlike the bulk of the peripheral T cells, which had a Thy1-, CD45RC+, and/or RT6+ phenotype, these RTE were Thy1+, CD45RC-, and RT6-. Furthermore, two discrete subsets of RTE were defined: a major subset (approximately 95%) of CD4+ or 8+ (single positive), TCR-alpha beta hi T cells that resembled medullary thymocytes; and a minor subset (approximately 5%) of CD4+ and 8+ (double positive), TCR-alpha beta low T cells that resembled cortical thymocytes. The following evidence suggested that most if not all Thy1+ T cells in young adult rats are RTE and their immediate descendants: 1) thymectomy (but not sham thymectomy) selectively depleted Thy1+ T cells from lymph node within 3 to 7 days, even in adrenalectomized rats; 2) most FITC-labeled RTE differentiated into Thy1-, CD45RC+, RT6+ T cells within 7 days of release from the thymus; 3) transitional phenotypes of Thy1+ T cells, including Thy1low, CD45RC+, and RT6+, were observed in normal, as well as in intrathymic, FITC-injected rats; 4) most T cells in neonatal rats were Thy1+ and RT6-, whereas their descendants were Thy1- and RT6+. These experiments demonstrate that most RTE in normal rats are phenotypically (and presumably developmentally) immature at the time of release from the thymus, and progressively acquire the phenotypic attributes of more mature T cells post-thymically. These unique phenotypic attributes should expedite the isolation of RTE and their immediate descendants for definitive studies of their developmental and functional properties.     

Identification and characterization of B cell precursors in rat lymphoid tissues. I. Adoptive transfer assays for precursors of TI-1, TI-2, and TD antigen-reactive B cells

Quantitative adoptive transfer assays were developed to detect the precursors of TI-1, TI-2, and TD antigen-reactive B cells in rat lymphoid tissues. Studies on the immune responses in normal and athymic nude rats validate the use of TNP-lipopolysaccharide as a TI-1 antigen, TNP-Ficoll as a TI-2 antigen, and SRBC as a TD antigen in rats. The precursors to these immunologically competent B cells are detected, following transfer into irradiated histocompatible recipients, by their ability to generate expanded populations of antigen-reactive B cells capable of mounting antibody responses (splenic IgM plaque-forming cells) to these antigens. Maximal numbers of antigen-reactive B cells emerge in antigenically naive rats after an interval of 7-12 days following transfer of donor lymphoid cells and decline rapidly thereafter. The delayed responses in adoptive recipients reconstituted with spleen cells are proportional to the numbers of spleen cells transferred and are shown to be primarily donor derived using histocompatible Ig kappa chain alloantigen disparate rat strain combinations. The precursors of TI-1, TI-2, and TD antigen-reactive B cells are present in both donor spleen and bone marrow. However, precursor cells to TI-1 and TD antigens are largely absent from donor lymph node cells, whereas precursors to the TI-2 antigen are as prevalent in donor lymph node as in donor spleen. These results support the hypothesis that newly formed virginal B cells represent transient populations of precursor cells that undergo further proliferation and differentiation in the spleen before acquiring immunological competence. The results also suggest that the precursors of TI-2 antigen-reactive B cells differ developmentally from those of TI-1 and TD antigen-reactive B cells, and that the antigen-reactive progeny of these precursors require additional stimulation in order to join the pool of long-lived peripheral B cells.