Inability of mitogen-stimulated spleen cells from newborn mice to synthesize interleukin-2 receptors.

Spleen cells from newborn mice do not respond by proliferation to concanavalin A (Con A) or bacterial lipopolysaccharide (LPS) stimulation. This non-reactivity cannot be reversed to a positive response by exogenous interleukin-2 (IL-2). The stimulation with Con A of spleen cells from newborn mice, in contrast to cells from adult animals, does not result in synthesis of mRNA for inducible 55,000 molecular weight (MW) IL-2 receptors (IL-2R). The failure of neonatal spleen cells to synthesize IL-2R mRNA is an intrinsic property of the cells themselves, and it is not due to activity of natural suppressor cells present in newborn animals. Since the expression of functional IL-2R represents one of the early and pivotal events in immune cell activation, we propose that the inability to synthesize IL-2R may be one of the primary reasons for the immunological immaturity of newborns.