Long-term decrease of CD4(+)CD45RA(+) T cells and impaired primary immune response after post-traumatic splenectomy

Congenital or acquired absence of the spleen and functional hyposplenism ar e associated with abnormalities of host defence such as an increased suscep tibility to infection with encapsulated bacteria. The effects of the lack o f the spleen on cell-mediated immunity are largely unknown. In the present study we have investigated peripheral blood lymphocyte subpopulations in he althy adults who had undergone splenectomy because of severe abdominal trau ma >4 years before the study. The results show a significant reduction in t he percentage of CD4(+) T cells due to a selective and long-term decrease i n the percentage of CD4(+)CD45RA(+) lymphocytes, the CD4(+) T-cell subset m ainly involved in primary immune responses to newly encountered antigens. L evels of the reciprocal CD45RO(+)CD4(+) T-cell subset were comparable betwe en splenectomized and control individuals, as were lymphoproliferative resp onses and IFN-gamma production to recall antigens. Decreased levels of CD4( +)CD45RA(+) cells were accompanied by an impairment in primary immune respo nsiveness, as assessed by investigating T-cell proliferation to stimulation with keyhole limpet haemocyanin and by measuring antibody responses follow ing primary immunization with a clinically relevant T-dependent antigen, he patitis A vaccine, in vivo. These findings suggest a possible role of the s pleen in the generation, maintenance and/or differentiation of naive, unpri med T cells or their precursors, which might have a possible functional rel evance for primary immune responses following splenectomy.