CD4 and infection: Infection-induced changes in cell numbers also resulted in a significant lowering of the brain CD4+/CD8+ T-lymphocyte ratio, decreasing from 1.04 ± 0.05 (mean ± SEM, n=6) in uninfected mice to 0.56 ± 0.06 (n=12) 1 mo after infection with Lm 10403s and from 0.79 ± 0.06 (n=8) in uninfected mice to 0.46 ± 0.04 (n=12) 4 mo after Lm 10403s infection.