Long-lasting recall response of CD4(+) and CD8(+) alpha beta T cells, but not gamma delta T cells, to heat shock proteins of Francisella tularensis

Decades after recovery from tularemia, circulating alpha beta T cells are k nown to still recognize a variety of membrane proteins of Francisella tular ensis. We studied the T cell response to 3 cytoplasmic heat shock proteins of the organism: DnaK, chaperone-60 (Cpn-60) and Cpn-10. Determination of s ubpopulations of responding T cells was of special interest as it has been suggested that homologs of these conserved proteins may be recognized by hu man gamma delta T cells. Compared with reference subjects with no history o f tularemia or tularemia vaccination, subjects who had been infected with t ularemia 10-30 y earlier showed a significantly (p = 0.01) higher prolifera tive T cell response to all 3 heat shock proteins. In general, the magnitud e of responses of CD4 T cells was higher than that of CD8 T cells. By flow cytometry, blast cells were shown to express the alpha beta T cell receptor . Under conditions that allowed vigorous expansion of gamma delta T cells i n response to a phosphorylated non-peptide antigen, no expansion of gamma d elta T cells occurred in response to DnaK or Cpn60 of F. tularensis. In con clusion, a long-lasting recall response to heat shock proteins of F. tulare nsis was demonstrated in alpha beta T cells but not in gamma delta T cells. The results support the assumption that human alpha beta T cells recognize bacterial proteins irrespective of the nature or localization of the prote ins in the bacterial cell and thereby contribute to the maintenance of a lo ng-lasting broad T cell response based on a wide variety of specificities.