Activation of cell-mediated immunity following immunization with pneumococcal conjugate or polysaccharide vaccine

The immunogenicity of pneumococcal polysaccharide (PS) vaccines can be impr oved by conjugating PS to a polypeptide carrier that alters the immune resp onse from T-cell independent to T-cell dependent. In order to study the inf luence of PS or protein antigens as inducers of cell-mediated responses, 30 adults were immunized with a 23-valent pneumococcal PS vaccine (PS-group) or an Ii-valent, tetanus and diphtheria mixed carrier conjugate vaccine wit h (adjuvant group) or without aluminium adjuvant (nonadjuvant group). Cell- mediated responses were analyzed on days 0, 14 and 28 after vaccination by measuring lymphocyte proliferation and production of interferon (IFN)-gamma (Th1 marker) or interleukin (IL)-4 and IL-5 (Th2 markers) cytokines after in vitro stimulation with the PS and protein components of the vaccines. Te tanus and diphtheria proteins were the main inducers of lymphocyte prolifer ative and cytokine responses. Conjugate vaccines induced increased prolifer ative responses to the tetanus or diphtheria protein, but not to the PS com ponents. In the PS-group, a lymphocyte proliferative response to protein an tigens was not observed. The number of antigen-specific and nonspecific IFN -gamma -secreting cells detected by ELISPOT tended to increase in all three groups in response to protein or to PS antigen. No major differences were detected in the number of IL-4-secreting cells measured 14 and 28 days afte r vaccination. The conjugate vaccine with adjuvant was associated with Th2 type of activation indicated by an enhanced IL-5 secretion in response to t he tetanus and diphtheria protein antigens.