Abstract
Lymph follicles (LF) have been viewed as nests for B cell proliferation and differentiation into memory cells. This report demonstrates that T cells in LF can also divide. We examined lymph follicles of immunized mice by immunohistochemical and autoradiographic techniques. We were able to detect subgroups of T cells in the S phase and localize them. From 0.2% to 0.5% of intrafollicular T cells incorporated 3H-thymidine and thus could have been in the S phase; such cells were found in every part of the follicle. Not only CD4+ T cells but also CD8+ T cells in LF incorporated 3H-thymidine. This study is the first to demonstrate a proliferation of CD8+ T cells in secondary lymph follicles. However, the ratio of CD4+ to CD8+ T cells in the S phase differed between LF and T-dependent zones; the ratios were 0.66 in LF and 1.78 in T zones. The difference may stem from differences in their immune response roles. When we counted the dividing T cells in the T-dependent zones, we found more of them in areas adjacent to the follicles than in more-distant areas. This suggests that T cells, engaged in the cell cycle in the T-dependent zones, moved toward the germinal center or actually entered it.
