Do carbohydrate antigens stimulate human T cells? Review article.

T cells fail to recognize free antigenic determinants. What the T-cell receptor recognizes is a complex consisting of a peptide fragment cleaved from antigen and self-MHC structures on the surface of antigen-presenting cells. While extensively investigated with protein antigens, only limited information is available on the capability of T cells to recognize carbohydrate antigens in a specific way. Therefore, we have investigated the specificity of human T-cell lines and clones reactive to streptococcal A (Strep A) vaccine. It was found that neither soluble streptococcal A carbohydrate (A-CHO) nor synthetic oligosaccharides deduced from bacterial carbohydrates could stimulate Strep A-reactive T cells, although A-CHO stimulates specific antibody production in B cells very effectively. In conclusion, Strep A-specific T cells seem to recognize other structures of the bacterial vaccine than A-CHO. This was confirmed by retained stimulation after removal of carbohydrate epitopes by periodate treatment. Such Strep A-reactive T cells are frequently (greater than 10(-3] found in CD4+ T cells of healthy donors. Implications of this finding with regard to anti-carbohydrate immune responses are discussed.