Antigen from Francisella tularensis: nonidentity between determinants participating in cell-mediated and humoral reactions.

After tularemia vaccinations, most individuals respond with cell-mediated and humoral immunity as disclosed by the lymphocyte stimulation test and enzyme-linked immunosorbent assay (ELISA), respectively. There is, however, no correlation between the magnitudes of the two responses, and some individuals show one of the responses only. We now report that the two responses are directed towards different antigenic determinants of the bacterium. Ether-water extraction of the live vaccine strain of Francisella tularensis gave a high yield of material reacting in ELISA as well as in the lymphocyte stimulation test. However, the specificity of the extract was low insofar as it reacted not only with lymphocytes and antibodies of tularemia-vaccinated individuals but also to a fairly high extent with those of nonvaccinated individuals. By using the extract as a starting material, a preparatory procedure was developed, resulting in antigen of high specificity in the two tests. The antigen prepared was a high-molecular-weight, carbohydrate-protein complex. Proteinase K treatment of the antigen abolished the lymphocyte-stimulating activity but did not decrease ELISA activity at all. Periodate treatment, on the other hand, greatly reduced ELISA activity but did not decrease the lymphocyte-stimulating activity. Thus, determinants of F. tularensis responsible for immunospecific lymphocyte stimulation seem to reside in protein, whereas ELISA activity seems to be due mostly to carbohydrate determinants.