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The humoral and cellular mechanisms effective<br />
for killing tumor cells in vitro<br />
Vladimir Kotnik 1 , Katarina Jordan 1 , Katarina Pirc 1 , Srdjan Novakovi} 2<br />
1<br />
Institute of Microbiology and Immunology, Medical Faculty, University of Ljubljana,<br />
Korytkova 2, 1000 Ljubljana, Slovenia, 2 Institute of Oncology Ljubljana, Zalo{ka 2, 1000<br />
Ljubljana, Slovenia<br />
Aim of the presentation is to discus different humoral and cellular mechanisms of<br />
surveillance and defense against tumors.<br />
Material and methods: Rabbit antibodies directed against membrane antigens of<br />
K562 cells were produced and used to make K562 – anti K562 antibodies immune<br />
complexes. Guinea pig complement finally diluted 1:10 was used to trigger the<br />
apoptosis and the cell death of target cells. Apoptosis and cell death were detected<br />
by the flow cytometry employing Annexin V test. The same kind of experiment was<br />
used on CD20+ Raji cells. Anti CD20 humanized monoclonal antibodies were used<br />
to make immune complexes. Human complement finally diluted 1:5 was added to<br />
induce apoptosis and cell killing. Effect was detected by Annexin V test also. The<br />
same target cells were used to asses effects of nonprimed fresh human PBMC. The<br />
Annexin test was used to detect a possible synergistic action of complement and<br />
PBMC induced cell death.<br />
Results: Clear proapoptotic and cytotoxic activity of complement was detected in<br />
both models. PBMC were cytotoxic also, but in a lesser degree than complement.<br />
Synergistic effect of both ways of cytotoxicity was not observed.<br />
Discussion: Tumor cells induced immune response and the production of specific<br />
antibodies directed against selected tumor antigens. These antibodies together with<br />
34l19<br />
complement induce apoptosis and cell cytotoxicity of antibody specific tumor cells.<br />
Tumor cells labeled with specific antibodies activate nonprimed PBMC obviously<br />
via ADCC mechanisms resulting in apoptosis and cell death. However, the tested<br />
mechanisms were functional and very effective in described models, several<br />
investigators reported, that tumor cells are able to escape from destruction using<br />
distinctive strategies, like changing or shedding of specific antigens, developing<br />
inhibitory regulatory molecules able to stop functioning of killer cells or complement<br />
activation, making tolerogenic surfaces etc.