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Cell-free extracts of disrupted Renografin-purifiedRickettsia typhi andR. prowazekii were evaluated as antigens in lymphocyte transformation assays for cell-mediated immunity to typhus group rickettsiae in 19 individuals with and 9 without histories of exposure to these organisms. Exposure consisted of clinical disease, vaccination with epidemic typhus vaccine, or occupational exposure to these agents. Both the soluble and membrane fractions of disrupted purified rickettsiae were used, and transformation of peripheral blood lymphocytes (PBL) was determined in microcultures by incorporation of [3 ]thymidine. Of the antigen concentrations tested (1 to 400 μg/ml), 10μg/ml appeared to be the most satisfactory. At this concentration, PBL transformation was highly reproducible and correlated well with donor exposure and the presence of enzyme-linked immunosorbent assay anti-typhus group immunoglobulin G. At higher concentrations, PBL from both exposed and control donors often responded to a lipopolysaccharide-like component present in these preparations. Specific transformation responses to rickettsial fractions were detected in several individuals decades after infection or vaccination, indicating that both fractions contained antigens associated with persisting cell-mediated immunity in humans. Generally, stimulation indexes with the soluble fraction were slightly greater than those obtained with corresponding concentrations of the membrane preparation, and in three individuals transformation was observed only with the soluble fraction. PBL transformation to soluble fractions also appeared to have some species specificity, since PBL from individuals with documentedR. typhi infections were more responsive to the homologous soluble preparation than to the soluble fraction ofR. prowazekii . PBL transformation also correlated well with homologous but only poorly with heterologous enzyme-linked immunosorbent assay immunoglobulin G titers.

In Vitro Stimulation of Human Peripheral Blood Lymphocytes by Soluble and Membrane Fractions of Renografin-Purified Typhus Group Rickettsiae