In situ kinetic analysis of thyroid lymphocyte infiltrate in mice developing experimental autoimmune thyroiditis

L3T4⁺ T cells from genetically susceptible mice developing experimental autoimmune thyroiditis (EAT) were shown earlier to proliferate in response to restimulation with mouse thyroglobulin (MTg) in vitro and to mediate the adoptive transfer of EAT, whereas Lyt-2⁺ cells differentiated in vitro into cells cytotoxic for thyroid monolayers. Leukocyte suspensions from disrupted thyroid glands examined on Days 13-21 after immunization revealed the accumulation of both T cell subsets in the infiltrate at varying ratios. To characterize the in situ kinetics of cellular infiltration in chronic EAT, we extended the observation intervals after immunization to include Days 21 to 42. The leukocytes in thyroid sections were labeled immunohistochemically first with rat monoclonal antibodies to L3T4, Lyt-2. Thy-1, k light chain, or F4 80 macrophage antigen, then with biotinylated anti-rat IgG, utilizing the avidin-biotin-peroxidase technique. Throughout the 21- to 42-day interval, no significant variations were detected in the percentages of L3T4⁺ subset, but those of Lyt-2⁺ cells increased and then declined. The shift in the L3T4⁺:Lyt-2⁺ ratio, down from 2.4 to 1.6 and then up to 3.0, was directly related to changes in the Lyt-2⁺ subpopulation. The F4 80⁺ and B cell populations changed little during this period. These findings illustrate the changing kinetics of T cell subsets in situ in the development and perpetuation of EAT and MTg-immunized mice.