MURINE T-CELL RESPONSE TO NATIVE AND RECOMBINANT PROTEIN ANTIGENS OF RICKETTSIA-TSUTSUGAMUSHI

A polyclonal T-cell line with TH1 characteristics was used to assess t he murine cellular immune response to native and recombinant Rickettsi a tsutsugamushi antigens. Proliferation of this T-cell line was observ ed in response to numerous native antigen fractions, which indicates t hat the murine T-helper-cell response is directed at multiple scrub ty phus antigens with no apparent antigenic immunodominance. Subsequent a nalysis of recombinant R. tsutsugamushi antigens made it possible to i dentify a 47-kDa scrub typhus antigen (Sta47) that was stimulatory for the polyclonal T-cell line. Recombinant clones encoding 56-, 58-, and 110-kDa antigens (Sta56, Sta58, and Sta110, respectively) were unable to induce proliferation of this T-cell line. DNA sequence analysis of the cloned rickettsial insert encoding the Sta47 protein revealed the presence of four open reading frames potentially encoding proteins of 47, 30, 18, and 13 kDa. Analysis of sodium dodecyl sulfate-polyacryl- amide gel electrophoresis-separated and eluted fractions of lysates fr om the recombinant HB101(pRTS47B4.3) demonstrated that the fractions c ontaining the 47-kDa protein as well as those containing proteins less than 18 kDa were stimulatory. Selected synthetic amphipathic peptides derived from the Sta47 antigen sequence identified a 20-amino-acid pe ptide that gave a 10-fold increase in T-cell proliferation over a cont rol malarial peptide of similar length. Recognition of the 47-kDa anti gen by a T-cell line with TH1 characteristics implicates this protein as one of potential importance in protection studies and future vaccin e development.