Interleukin-2 dependent selective activation of porcine γδ T lymphocytes by an extract from the leaves of Acanthospermum hispidum.
The immunostimulatory capacity of A. hispidum, a tropical plant which is used in the traditional medicine of Benin for the treatment of infectious diseases, was studied in the porcine immune system. These in vitro studies revealed the capacity of A. hispidum to enhance the proliferation of T lymphocytes after stimulation with ConA or allogeneic stimulator cells in the mixed leucocyte culture (MLC). The virus-specific MHC class II-restricted in vitro immune response against pseudorabies virus (PRV) was also enhanced in a co-stimulating manner. Phenotyping of T lymphocytes that had been activated in vitro in the presence of A. hispidum revealed an increase of activated γδ T lymphocytes with the phenotype CD2-CD5low+CD8-. In vitro analysis of the influence on the lymphocyte function demonstrated neither an increase of the immunoglobulin synthesis, nor of the interleukin-2 production, nor of the cytolytic activities. Experiments using separated T-lymphocyte subpopulations showed that the co-stimulatory activity was based on a synergism between T helper and γδ T lymphocytes, and that γδ T lymphocytes were the targets of the plant-derived extract. The γδ T cells which could not be activated in mixed leukocyte cultures or with pseudorabies virus antigen in a secondary immune response, were reactive to the interleukin-2 released from antigen-stimulated T helper lymphocytes. A. hispidum enhanced the responsiveness of γδ T lymphocytes to IL-2.