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The ontogeny of the human immune system was studied by analyzing fetal and adult tissues for the presence of various lymphocyte populations and activation/maturation markers. CD95 (fas) was expressed in hematopoietic tissues during the final stages of development of monocytes, granulocytes, NK cells and T cells, but to a much lesser extent on B cells. In the periphery, CD95 expression declined on granulocytes and NK cells. CD95 was expressed at a higher level on CD45RA+ peripheral T-cells in the fetus than in the adult. Contrary to the belief that most fetal T-cells are naı¨ve or resting, a notable number of CD45RO+ T-cells were observed as well as an unique CD95−CD45RO+ population. Activation markers CD25, CD122, CD69 and CD80 were also present on fetal T-cells. These findings indicate that in the initial weeks following thymic maturation, a high frequency of T-cells is activated in the periphery of the fetus. [Copyright &y& Elsevier]

Nonspecific cytotoxic cells (NCC) are a type of teleost NK-like cell. In the present study a novel stimulus secretion model is described for catfish NCC utilizing single base oligodeoxyguanosine. Binding of guanosine 20-mers (dG20) to NCC up-regulated expression of cytosolic FasL detected by an anti-human FasL monoclonal antibody (mab). In vitro treatment of purified NCC with dG20 produced a 7-fold increase in expression of soluble Fas ligand (sFasL) after 3 h. Antibody binding to NCC was saturable and approximately 30–35% of total NCC were positive for sFasL expression. The teleost FasL equivalent produced programmed cell death of appropriate FasR positive targets. Supernatants from dG20 activated NCC produced hypoploidy and annexin-V binding by FasR bearing HL-60 cells. Treatment of activated supernatants with immobilized anti-FasL mab neutralized these activities. These studies demonstrated that an NK like cell (NCC) produces and secretes sFasL following binding by single base oligodeoxyguanosine. [Copyright &y& Elsevier]

Understanding the immunological function of bovine γδ T cells is essential for evaluating their role in the response to infectious agents and for determining the potential of targeting this population with vaccines. This study examined the age dependent changes of circulating CD2+ and CD2− γδ T cells as well as differences in the expression of activation markers between these two populations. Changes in activation marker expression following vaccination with Vira Shield® 5 are also discussed. CD62L was expressed on all CD2− γδ T cells but only a subset of CD2+ γδ T cells and following vaccination there was a significant decrease in the percentage of CD2−/CD62L+ γδ T cells but not CD2+/CD62L+ γδ T cells. Both CD2− and CD2+ γδ T cells consistently expressed high levels of CD44. The majority of both CD2− and CD2+ γδ T cells also expressed CD45R, however, more of the CD2− cells were CD45Rneg/lo. Following vaccination there was a significant decrease in the percentage of CD2− and CD2+ γδ T cells that expressed CD44 and CD45R. These data indicate significant differences in activation expression on CD2− and CD2+ γδ T cells, which adds to the growing evidence that there may be functional as well as phenotypic differences between these two populations of bovine γδ T cells. [Copyright &y& Elsevier]