Macrophage Inhibition Produced by Guinea Pigs after Sensitization with a Larval Antigen of Trichinella spiralis

Abstract

Experimental guinea pigs were sensitized both with a protein fraction of T. spiralis larvae (Melcher's antigen) and M. tuberculosis H37Ra in Freund's complete adjuvant. Controls were injected with the adjuvant alone. The experimental animals showed typical delayed skin reactions of the tuberculin type in separate sites tested with Melcher's antigen and Purified Protein Derivative (PPD), whereas the controls reacted only to PPD. Studies were made with peritoneal exudate cells to determine the effect of Melcher's antigen and PPD on macrophage inhibition in capillary tubes. The macrophages from all of the experimental animals were inhibited strikingly by both Melcher's antigen and PPD, but those from the control animals were inhibited only by PPD. These results suggest that in mice Melcher's antigen might increase the reproducibility of the inhibition test results shown previously with a crude saline extract of T. spiralis larvae. There is considerable evidence to support the suggestion that immunity to the intestinal stages of T. spiralis in the mouse host is due to delayed (cellular) hypersensitivity (Larsh, 1967). Recently, a crude saline extract of T. spiralis larvae has been used as a means for artificially sensitizing donors so that this immunity could be studied under more controlled conditions than are possible when using infected mice for this purpose. Donors sensitized with this crude antigen produced immunity, and after transfer of their spleen cells, immunity was conferred upon recipients (Larsh et al., 1969, 1970a, b). Although the results of these cell transfer studies tend to support the view that the transferred cells produced delayed sensitivity in the recipients, more information is needed to prove this hypothesis. In the first place, it must be shown that the sensitized donors have, in fact, developed delayed sensitivity as result of these antigen injections. Various in vivo tests are available for this purpose, such as skin and footpad tests. However, in view of its great potential value in such studies, and its acceptance as an in vitro correlate of delayed hypersensitivity, we chose first to make tests in capillary tubes for the inhibition of migration of macrophages. In 60% of the tests, the crude saReceived for publication 30 July 1970. * This investigation was supported in part by the Postdoctoral Fellowship (1F02GM44719-01, National Institute of General Medical Sciences) of the senior author. line extract antigen in the presence of splenic lymphocytes from artificially sensitized mice inhibited the migration of macrophages (Cypess and Larsh, 1970). The failure to obtain inhibition in a greater percentage of tests was attributed tentatively to the use of a crude antigen. Therefore, it was decided to select a more refined antigen for a similar study. The only reports to date on delayed skin responses to T. spiralis antigens in experimental hosts have dealt with studies in guinea pigs (Kim, 1966; Kim et al., 1967a, b). In these studies, a saline extract antigen similar to the one mentioned above was used for the most part, but some work was done by Kim (1966) with a more refined substance (Melcher's antigen), which is an acid-soluble protein fraction. Delayed skin reactions of the tuberculin type were demonstrated with both antigen preparations. In view of the available information on Melcher's antigen in guinea pigs, it was decided to use this system for the present study of macrophage inhibition. It seemed advisable to include an organism (Mycobacterium tuberculosis) known to produce consistently both delayed skin reactions and macrophage inhibition in tests with sensitized guinea pigs. This provided a means for checking the effectiveness of our sensitizing procedures, and the specificity of the responses produced as tested by skin reactions and inhibition of migration of