Mechanisms of the immune system in fighting tumours and the causes of their failure

One of the principal biological function of the immune system is a surveillance over our integrity endangered by malignant process. The immune system is endowed by a spectrum of various effector mechanisms, which provide various cells of the immune system, especially activated M1 macrophages, NK cells and cytotoxic T cells, and, in less extent, also antibodies. Nonetheless, in some cases, tumour cells can escape of their demise. They modify their microenvironment, they recruit cells with immunosuppressive activities like MDSC (myeloid derived suppressor cells), regulatory T cells, M2 type of macrophages and they themselves produce immunosuppressive substances, express of immune-checkpoints for T cell activation, and others. The greatest problem on fighting tumours is ability of tumour cells to metastasize. Metastatic process is not an accidental process; contrariwise, it is regulated by mechanisms known as epithelial to mesenchymal transition. It comprises release of a malignant cell from neighbouring cells, transition from its epithelial to mesenchymal shape, receiving increased mobility and ability to penetrate through a tissue and entering the circulation. The principle role in this transmigration play interactions between adhesive molecule in membranes of tumour cells and those present in membranes on endothelial cells of the organ they wish to settle in. Metastatic process can be mediated by exosemes too. (author)