Aging effects on secretory IgA immune responses.

Studies of cellular and humoral components of the secretory immune system indicated dramatic decreases in the SIgA response to T-dependent antigens (i.e. DNP-BGG) in aged rats. Senescent rats (18-20 months old) showed comparable levels of SIgA anti-DNP antibody to adult animals after oral immunization with a T-independent antigen, DNP-FICOLL. The salivary SIgA responses to both antigens were substantially decreased in weanling rats (21-35 days) versus the adult rats. Significant anamnestic SIgA responses were shown after oral immunization with DNP-BGG in adult rats, but was not observed in the senescent and midlife (10-12 months) rats. In contrast, the DNP-FICOLL appeared incapable of eliciting a secondary SIgA response in any of the groups. Examination of immunoglobulin-containing cells (ICC) in secretory and lymphoid tissues indicated a generally decreased proportion of IgAICC and IgGICC in the secretory tissues from the senescent rats. IgAICC and IgGICC were within normal limits in the lymphoid tissues of the senescent rats. The results demonstrate a defect in the ability of aged rats to manifest an IgA response to T-dependent antigens administered at mucosal surfaces.