Mice infected with Trypanosoma brucei, the causative agent of human sleeping sickness and a contributor to nagana in cattle, rapidly lose the capacity to mount VSG-specific antibody responses, and die with uncontrolled parasitemia. We have shown (Bockstal et al., 2011, PLOS Pathogens) that the loss of humoral immune competence in the infected mice results from depletion of developing and mature splenic B cells. We now report that T. brucei-induced splenic B cell depletion is dependent upon the presence of the pore forming molecule perforin which is present in the cytotoxic granules of cytotoxic T lymphocytes, natural killer T cells and natural killer cells, occurs in the absence of T cells (and natural killer T cells), i.e., in T cell receptor (αβγδ)-/- mice, but does not occur in intact mice that are depleted of natural killer (NK) cells by treatment with monoclonal antibody specific for the NK1.1 differentiation antigen. In the intact mice, B cells are deleted after remission of the first T. brucei parasitemic wave. At this time natural killer cells are expressing the cytotoxic granule marker CD107a, indicating that they have degranulated, executing their effector function. Moreover, in vitro assays show that B cells from T. brucei infected mice are killed by natural killer cells from uninfected C57BL/6 mice but not efficiently killed by CD107a positive natural killer cells isolated from infected mice, which may be functionally exhausted.

Laminitis is a chronic, crippling disease triggered by the sudden influx of dietary starch. Starch reaches the hindgut resulting in enrichment of lactic acid bacteria, lactate accumulation, and acidification of the gut contents. Bacterial products enter the bloodstream and precipitate systemic inflammation. Hindgut lactate levels are normally low because specific bacterial groups convert lactate to short chain fatty acids. Why this mechanism fails when lactate levels rapidly rise, and why some hindgut communities can recover is unknown. Fecal samples from three adult horses eating identical diets provided bacterial communities for this in vitro study. Triplicate microcosms of fecal slurries were enriched with lactate and/or starch. Metabolic products (short chain fatty acids, headspace gases, and hydrogen sulfide) were measured and microbial community compositions determined using Illumina 16S rRNA sequencing over 12-hour intervals. We report that patterns of change in short chain fatty acid levels and pH in our in vitro system are similar to those seen in in vivo laminitis induction models. Community differences between microcosms with disparate abilities to clear excess lactate suggest profiles conferring resistance of starch-induction conditions. Where lactate levels recover following starch induction conditions, propionate and acetate levels rise correspondingly and taxa related to Megasphaera elsdenii reach levels exceeding 70% relative abundance. In lactate and control cultures, taxa related to Veillonella montpellierensis are enriched as lactate levels fall. Understanding the microbial dynamics underlying lactic acidosis and laminitis will lead to better informed models of health and the development of a probiotic treatment to prevent acidosis.