Suppression of CD4+ T-cell expansion by P. chabaudi infection in vivo. (a) Uninfected (open bars) or P. chabaudi-infected (filled bars) BALB/c mice received DO11.10 T cells and remained unimmunized or were immunized with OVA/LPS 12 days post-infection. Expression of CD69 on splenic OVA-specific T cells was assessed 18 h post-immunization. Results shown are the proportion of OVA-specific CD4+KJ1.26+ T cells expressing CD69 and represent the mean of three mice per group ±1 s.d. (b) Uninfected (squares) or P. chabaudi-infected (circles) BALB/c mice were transferred and immunized (filled symbols) or remained unimmunized (open symbols) and the absolute number of OVA-specific T cells in spleen (left) and lymph nodes (right) calculated at various times. Results show the mean number of CD4+KJ1.26+ T cells and represent the mean of three mice per group ±1 s.d. (*p ≤ 0.05, #p ≤ 0.005 uninfected and immunized versus P. chabaudi-infected and immunized). (c) Representative CFSE profiles of OVA-specific T cells are shown (left) and data shown as the mean proportion of CD4+KJ1.26+ cells under each CFSE peak in uninfected (open bars) and P. chabaudi-infected (filled bars) following immunization (bottom histogram) or in unimmunized controls (upper histogram). Data represent the mean of 3 mice per group ±1 s.d. (*p ≤ 0.05, #p ≤ 0.005 uninfected and immunized versus P. chabaudi-infected and immunized).