CELLULAR-REQUIREMENTS FOR THE ACTIVATION AND PROLIFERATION OF RUMINANT GAMMA-DELTA T-CELLS

Requirements for the activation and proliferation of gamma delta T cel ls were investigated, Maximum numbers of gamma delta T cells expressed the IL-2R alpha-chain after 6-h Con A stimulation in peripheral blood , efferent lymph, and afferent lymph, In comparison, IL-2R alpha-chain expression on CD4 T cells only reached maximum levels in response to Con A stimulation in peripheral blood and afferent lymph populations, Analysis of enriched gamma delta T cells demonstrated that Con A-induc ed expression of the IL-2R alpha-chain was independent of APC, Togethe r, these data suggest that the requirements for gamma delta T cell act ivation are less stringent than those for alpha beta T cell activation , Unfractionated peripheral blood, efferent lymph, and afferent lymph cell populations proliferated in response to Con A alone, In contrast, enriched gamma delta T cells (CD4/CD8 depleted) from efferent lymph d id not proliferate in response to Con A alone, but required the additi on of IL-2, This requirement for exogenous IL-2 could be overcome by t he addition of dendritic cells purified from afferent lymph, These res ults suggested that gamma delta T cells required costimulatory signals provided by APC to ensure the production of sufficient IL-2 to drive proliferation, CD28 and CTLA-4 mRNA were detected in efferent lymph an d afferent lymph populations containing CD4 and CD8 T cells stimulated with Con A and IL-2 or with Con A alone, respectively, In contrast, n egligible levels of these mRNA species were detected in efferent and a fferent lymph populations devoid of CD4 and CD8 T cells, These results suggest that ovine gamma delta T cells may use alternative costimulat ory pathways.