CD40LG and infection: Several lines of evidence suggest that these are T-cell dependent GCs: (i) they exist for several weeks 33, (ii) they harbor as many T cells as the T cell dependent GCs induced after immunization with sheep red blood cells or after infection with L. major (Fig.4C), and (iii) injection of activated T cells into CD154-deficient hosts that are able to develop T-cell independent but not T-cell dependent GCs 28 does not lead to formation of GCs in the spleen (Fig.5B).