Social rearing conditions before weaning influence numbers and proportions of blood immune cells in laboratory rats

The influence of the early social rearing environment on blood cellular immunity was investigated in the male offspring of Long-Evans rats. Sons of females housed in pair groups (P-males) and sons of females living in a mixed sex colony (C-males) were studied. After weaning at the age of 21 days, offspring were housed individually to ensure identical experiences until the age of 100 days when immunological assessments were conducted. C-males had significantly higher numbers of blood CD4 and CD8 T cells as well as higher numbers of granulocytes and monocytes than P-males. In contrast, the number of B cells and NK cells was similar in P- and C-males. T-cell responsiveness to ConA, determined in the peripheral blood mononuclear cells and whole blood assays, did not differ significantly between the two groups. The study indicates that the early social environment affects numbers and proportions of many blood immune cell subsets in later life.