IL4 and infection: Co-infected cats also had accelerated anti-FIV capsid antibody development soon after FIV infection when compared to cats with single PLV or single FIV infection [9], and multivariate analysis implicates immediate anti-PLV immune responses involving CD8+ T cells, CD25+ cells, IL-4, IFN-γ, and the death receptor (FAS) as correlates of attenuated disease in co-infected cats [10].