Blocking antigen-presenting cell/T cell interaction by monoclonal antibodies

During activation of the adaptive immune system, antigen presenting cells get in contact with T or B cells. They form the immunological synapse, in which antigen recognising molecules, costimulatory molecules and adhesion molecules play an important role. Adhesion molecules close the distance between these two cells, to establish prolonged contact and to achieve antigen recognition by the adaptive immune system. The formation of the immunological synapse is also essential for memory cell reactivation. Several molecules act in this synapse, of which six were investigated more closely in this thesis: CD2 acts as an adhesion molecule with powerful costimulatory properties. CD11a and CD18 form the lymphocyte function-associated antigen 1 (LFA-1), one of the most important adhesion molecules during synapse formation. CD50 on the other hand is assumed to be one of the first adhesion molecules involved in synapse assembly. CD4 and MHC-II are important molecules for antigen recognition and therefore form the core of the immunological synapse. During our studies on porcine peripheral blood mononuclear cells, naive T cells, memory T cells and myeloid cells were first phenotypically characterised using flow cytometry, to describe the distribution of the above-mentioned molecules on the different cell types. Our results show, that CD2 can be primarily found on naive and memory T cells and only in very low amounts on myeloid cells. CD11a and CD18 are present on almost all myeloid cells, naïve T cells and memory T cells. CD50 can be found on approximately 60 % of myeloid cells, about 10 % of naïve T cells, and 15 % of memory T cells. For our second experimental setup, cells from pigs that have been immunised with either an ovalbumin formulation (OVA) or porcine circovirus type 2 (PCV2) vaccine (Ingelvac CircoFLEX®, Boehringer Ingelheim Vetmedica GmbH) were used. Antigen-specific re-stimulation in in-vitro assays were performed to induce activation and proliferation of memory T cells. In addition, monoclonal antibodies (mAbs) directed against the above-mentioned molecules were added to the setup, to investigate whether activation can be blocked/reduced by interfering with one of these molecules. Using a proliferation dye (CellTraceTM Violet solution), the proliferative response to the stimulus could be assessed. We looked for changes in memory-cell proliferation within CD4 T cells, but also monitored changes in other T-cell subsets like cytolytic T cells and TCRγδ T cells. Even though changes in memory cell proliferation were difficult to interpret, the percentage of CD4+ cells within all T cells proved to be a good indicator of a potential effect of the used antibodies. The anti-CD2 mAb led to a considerable decrease in CD4+ T cells, cytolytic T cells and proliferating Th memory cells. Even though this effect was visible in both, animals immunised with OVA or with PCV2, the effect was more noticeable in PCV2 animals. The anti-CD4 mAb also resulted in a drop in CD4+ T cells and proliferating Th memory cells without decreasing the frequency of cytolytic T cells. Anti-MHC-II mAbs did not seem to influence frequencies of the investigated T cell subsets, but also led to a decrease in Th memory cell proliferation in PCV2 animals. These results suggest, that besides molecules involved in antigen recognition, especially CD2 plays an important role during memory cell reactivation. The other tested antibodies did not seem to obviously effect the reactivation of memory cells and overall T cell populations.