Introduction, how can we study the immune system ?

The first lecture included an introduction recalling the main effector mechanisms of innate immunity (passive and active physical barrier, secretory and cellular responses) and adaptive immunity (function of T and B lymphocytes). We then discussed the fundamental and medical issues that "justify" seeking to characterize the "state of health" of the immune system of a living being or population. The various approaches to analysis were presented, highlighting the decisive technological advances made in recent years: from phenotypic analysis by flow cytometry in the 1980s and the multi-parametric analysis possibilities offered by the use of spectral deconvolution of fluorescence radiation emitted by fluorochromes coupled to monoclonal antibodies, to mass spectrometry analysis of heavy metals coupled to antibodies attached to the cells of interest. The use of biphoton microscopy now makes it possible to visualize in vivo in animals the behavior of immune system cells, for example during their activation in a secondary lymphoid organ. It is now possible to combine this dynamic visualization with functional imaging that objectifies activation events or biological responses such as cytotoxicity or cytokine production. A third line of research concerns the study of gene expression profiles by particular cell type, as a function of a given stimulation. Coupled with analysis of the polymorphism of genome variants within a given population, this makes it possible to highlight "cis" and "trans" correlations between given genetic sequences and the degree of gene expression. This work could make it possible to identify key molecular pathways involved in responses to microorganisms, as well as their genetic variability (likely to explain vulnerability/resistance to certain infections and correlated with risk factors for autoimmune or inflammatory pathological responses). Analyses of these large-scale data, combined with qualitative and quantitative determination of the microbes (bacteria, viruses...) present in the skin, mucous membranes or blood, are thus beginning to help determine the "state of health" of the immune system.