T cells are essential for inducing clonal B cell expansion in germinal
centers during T cell-dependent antibody responses. However, class-sw
itched antibodies are readily detectable in TCR alpha-deficient mice t
hat congenitally lack crp T cells, including those such as IgG1 that a
re considered to be dependent on collaboration between B cells and alp
ha beta T cells. This observation suggests that a novel form of B:T co
llaboration may be evident in TCR alpha(-/-) mice. We report that germ
inal centers develop spontaneously in mice lacking T cell receptor ct
genes (TCR alpha(-/-)), despite the absence of alpha beta T cells. The
y are not seen in TCRB(-/-) mice kept in similar conditions. Both stra
ins of mice have gamma delta T cells, but it is a subset of T cells ex
pressing TCR beta and CD4 that is dominant in the germinal centers of
TCR alpha(-/-) mice. Exceptionally, germinal centers were associated w
ith CD4(+) gamma delta T cells. The expression of CD4 seems to be impo
rtant, for few extrafollicular T cells have CD4 and CD4 is largely abs
ent from TCR beta(-/-) T cells. The CD4(+) TCR beta cells may help B c
ells produce autoantibodies that have been identified in TCR alpha(-/-
) mice.