CD4 and infection: Actually, in terms of lymphocyte populations it was shown that an increase in the CD4 : CD8 ratio and IgG1 was associated with self-cure in T. evansi-infected sheep, whereas a decrease in the CD4 : CD8 ratio and IgM associated with an increase in the number of sIg+, CD45R+, CD1+, a major histocompatibility complex (MHC) II+ circulating B cells, was associated with infection and disease development [186, 190].