[Cell cooperation in immune responses]

All immune responses are assisted by different subpopulations of cells with complementary properties. Beside T and B lymphocytes specialized into effector killers, pro-inflammatory or antibody-producing cells, there are accessory and helper cells which exert various functions, such as antigen degradation and presentation, activating signal amplification and support of antigen-activated lymphocytic clones expansion and their functional differentiation. These cells, whose role is to co-operate with effector lymphocytes, are either lymphocytes, such as antigen-presenting B cells and helper T cells, or cells of haematopoietic origin belonging to the monocytic lineage, such as macrophages, monocytes and dendritic cells. Co-operation between subpopulations of the immune system takes place either by cell-to-cell interactions, or by indirect interactions via soluble mediators. Direct interactions postulate the involvement of receptor molecules and ligand-molecules expressed at cell surface. Indirect interactions are mediated by cytokines secreted by accessory or helper cells and acting at short distance to the point of secretion. Surface molecules and cytokines are well characterized both biochemically and functionally, and we are now in a position to manipulate the essential stages of cellular or hormonal immune response by using either cytokines and their inhibitors, or agonists or antagonists of surface receptors. Co-operation between cells participates in the autoregulation of the immune system. Through modulation of surface molecules and synthesis of cytokines the immune system can amplify discreet signals or repress untimely responses.(ABSTRACT TRUNCATED AT 250 WORDS)