AVIAN COCCIDIOSIS - CHANGES IN INTESTINAL LYMPHOCYTE POPULATIONS ASSOCIATED WITH THE DEVELOPMENT OF IMMUNITY TO EIMERIA-MAXIMA

The effect of infection and subsequent challenge with Eimeria maxima o n the populations of lymphocytes in the small intestine of Light Susse x chickens was assessed by immunohistochemistry. T cells were characte rized for CD3, CD4, CD8, TCR1 (gamma delta heterodimer) or TCR2 (alpha beta(1) heterodimer) markers, and B cells for the expression of IgM, IgA and IgG. After a primary inoculum there were, in both the epitheli um and the lamina propria, two distinct increases in the numbers of T lymphocytes. The first peaked on days 3-5 and the second greater influ x, on day 11 after infection. CD4(+) and CD8(+) cells were represented in both peaks but, whereas CD4(+) cells were found almost exclusively in the lamina propria, CD8(+) cells were present in both sites. The a rea staining positive for CD8(+) cells was somewhat greater than the v alue obtained for CD4(+) cells. In the epithelium there was an early, small increase in TCR1(+)-staining, followed by a larger rise to the s econd peak, at which time there was also an increase in the lamina pro pria. Staining for TCR2(+) cells followed the same pattern with a reve rsed distribution between epithelium and lamina propria. Changes after challenge were minimal mid confined to the epithelium. The most notab le changes in the expression of immunoglobulins were, in the lamina pr opria, a biphasic increase in the amount of IgM(+)-staining in the cou rse of primary infection (corresponding approximately to that of the T cells), and in IgA(+) cells shortly after challenge.