Role of CD4+ T Cells in the Control of Viral Infections: Recent Advances and Open Questions

CD4+ T cells orchestrate adaptive immune responses through their capacity to recruit and provide help to multiple immune effectors, in addition to exerting direct effector functions. CD4+ T cells are increasingly recognized as playing an essential role in the control of chronic viral infections. In this review, we present recent advances in understanding the nature of CD4+ T cell help provided to antiviral effectors. Drawing from our studies of natural human immunodeficiency virus (HIV) control, we then focus on the role of high-affinity T cell receptor (TCR) clonotypes in mediating antiviral CD4+ T cell responses. Last, we discuss the role of TCR affinity in determining CD4+ T cell differentiation, reviewing the at times divergent studies associating TCR signal strength to the choice of a T helper 1 (Th1) or a T follicular helper (Tfh) cell fate.     

The Innate Immune Glycoprotein Lactoferrin Represses the Helicobacter pylori cag Type IV Secretion System

Chronic infection with Helicobacter pylori increases risk of gastric diseases including gastric cancer. Despite development of a robust immune response, H. pylori persists in the gastric niche. Progression of gastric inflammation to serious disease outcomes is associated with infection with H. pylori strains which encode the cag Type IV Secretion System (cag T4SS). The cag T4SS is responsible for translocating the oncogenic protein CagA into host cells and inducing pro-inflammatory and carcinogenic signaling cascades. Our previous work demonstrated that nutrient iron modulates the activity of the T4SS and biogenesis of T4SS pili. In response to H. pylori infection, the host produces a variety of antimicrobial molecules, including the iron-binding glycoprotein, lactoferrin. Our work shows that apo-lactoferrin exerts antimicrobial activity against H. pylori under iron-limited conditions, while holo-lactoferrin enhances bacterial growth. Culturing H. pylori in the presence of holo-lactoferrin prior to co-culture with gastric epithelial cells, results in repression of the cag T4SS activity. Concomitantly, a decrease in biogenesis of cag T4SS pili at the host-pathogen interface was observed under these culture conditions by high-resolution electron microscopy analyses. Taken together, these results indicate that acquisition of alternate sources of nutrient iron plays a role in regulating the pro-inflammatory activity of a bacterial secretion system and present novel therapeutic targets for the treatment of H. pylori-related disease.     

Plasticity of Intestinal Epithelium: Stem Cell Niches and Regulatory Signals

The discovery of Lgr5+ intestinal stem cells (ISCs) triggered a breakthrough in the field of ISC research. Lgr5+ ISCs maintain the homeostasis of the intestinal epithelium in the steady state, while these cells are susceptible to epithelial damage induced by chemicals, pathogens, or irradiation. During the regeneration process of the intestinal epithelium, more quiescent +4 stem cells and short-lived transit-amplifying (TA) progenitor cells residing above Lgr5+ ISCs undergo dedifferentiation and act as stem-like cells. In addition, several recent reports have shown that a subset of terminally differentiated cells, including Paneth cells, tuft cells, or enteroendocrine cells, may also have some degree of plasticity in specific situations. The function of ISCs is maintained by the neighboring stem cell niches, which strictly regulate the key signal pathways in ISCs. In addition, various inflammatory cytokines play critical roles in intestinal regeneration and stem cell functions following epithelial injury. Here, we summarize the current understanding of ISCs and their niches, review recent findings regarding cellular plasticity and its regulatory mechanism, and discuss how inflammatory cytokines contribute to epithelial regeneration.     

Different durations of whole raw soybean supplementation during the prepartum period: Measures of cellular immune function in transition cows

The objective of this study was to evaluate different durations of whole raw soybean (WS) supplementation (diet rich in n-6 fatty acid) during the prepartum period on cellular immune function of dairy cows in the transition period and early lactation. Thirty-one Holstein cows were used in a completely randomized design and assigned to 4 experimental groups (G) [G90, G60, G30, and G0 (control)] supplemented with a diet containing 12% of WS from 90, 60, 30 and 0 d relative to the calving date, respectively. Cows were dried off 60 d before the expected calving date. After parturition, all cows were fed a diet containing 12% of WS until 84 DIM. Blood samples were collected before the morning feeding (d ?56 ± 2, ?28 ± 2, ?14 ± 2, ?7 ± 2, at the day of partum, 7 ± 2, 14 ± 2, 28 ± 2, and 56 ± 2 relative to parturition). Cell phenotyping and phagocytosis assays were carried out using monoclonal antibodies and flow cytometry technique. Duration of WS supplementation linearly increased the percentage of blood CD3⁺ cells, as well as increased the percentage of blood CD8⁺ cells in the postpartum period, notably in G30, whereas the lowest values were observed in G0. Further, the duration of WS supplementation linearly increased the reactive oxygen species median fluorescence intensity of CH138⁺ cells after phagocytizing Staphylococcus aureus in the postpartum period. Longer periods of WS supplementation linearly increased phagocytosis median fluorescence intensity of CH138⁺ cells in the prepartum period of cows. Duration of WS supplementation linearly increased the percentage of blood CD14⁺ cells producing reactive oxygen species when stimulated either by Staph. aureus or Escherichia coli in the postpartum period. In conclusion, longer periods of WS supplementation during late lactation and the dry period (beginning on d 90 of the expected calving date) alter the leukocyte population and improve neutrophil immune response in the postpartum period with no detrimental effects on cow performance.     

Effects of different types of potato resistant starches on intestinal microbiota and short-chain fatty acids under in vitro fermentation

The prebiotic effects of potato resistant starches RS1, RS2, RS3a, RS3b and RS4 were studied using simulated gut fermentation in vitro. The intestinal microbial composition was significantly changed by resistant starch (RS) after 24-h fermentation. All RSs (P < 0.05) decreased the ratio of Firmicutes/Bacteroidetes (F/B), and RS2 exhibited the lowest value of 0.95 ± 0.07. The relative abundance of Bifidobacterium was significantly increased by RS4, whereas Megamonas and Prevotella were promoted by RS2. Further, RS4 produced the highest levels of acetate (138.34 µM), whereas RS2 produced the highest levels of propionate (41.45 µM) and butyrate (21.65 µM). However, Bifidobacterium did not promote the production of propionate or butyrate, even though it was proficient in fermenting RS. Megamonas and Prevotella were positively associated with the higher production of propionate and butyrate. Here, different RSs played key roles in promoting intestinal health, and RS2 especially showed more abundant probiotic functions.     

Metagenomic analysis revealed the individualized shift in ileal microbiome of neonatal calves in response to delaying the first colostrum feeding

The aim of this study was to explore the effect of colostrum feeding time on the ileal microbiome of neonatal calves. In this study, 22 male Holstein calves were randomly assigned to different colostrum feeding time treatments: after birth (at 45 min, n = 7); at 6 h after birth (n = 8); and at 12 h after birth (TRT12h; n = 7). At 51 h after birth, calves were killed and ileum digesta was collected for microbiome analysis using shotgun metagenomic sequencing. Bacteria, archaea, eukaryotes, and viruses were identified from the ileum microbiome. For the bacteriome, Firmicutes and Proteobacteria were the predominant phyla, and Escherichia, Streptococcus, Lactobacillus were the 3 most abundant genera. For the archaeal community, Euryarchaeota and Crenarchaeota were the 2 major phyla, and Methanosarcina, Methanobrevibacter, and Methanocorpusculum were the 3 most abundant genera. In total, 116 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were identified from the ileal microbiome, with “biosynthesis of vancomycin group antibiotics,” “biosynthesis of ansamycins,” “valine, leucine, and isoleucine biosynthesis,” “ribosome,” and “d-alanine metabolism” as the top 5 functions. When the ileal microbiomes were compared among the 3 treatments, the relative abundance of Enterococcus was higher in TRT12h calves, suggesting that calves may have a higher abundance of opportunistic pathogens when the feeding of colostrum is delayed for 12 h. Moreover, among all KEGG pathways, the enriched “taurine and hypotaurine metabolism” (KO00430) pathway was identified in the ileal microbiome of TRT12h calves; however, future studies are needed to understand the effect on the host. Additionally, 2 distinct ileal microbial profiles were identified across all samples, indicating that that host factors may play a significant role in driving varied microbiome changes in response to colostrum feeding time. Whether such microbiome shifts affect long-term gut function and calf performance warrants future studies.