One of the principles of adaptive immunity is that, following an immune response triggered by an infectious agent, "memory" T and B lymphocytes are generated, i.e. long-lived lymphocytes capable of generating a faster, more effective response to a new infection by the same (or a similar) microbial agent, neutralizing the infectious agent before it causes disease. This is the principle behind vaccination, immunology's most convincing achievement.
Memory T lymphocytes can be identified using membrane markers, making them much easier to analyze. In this way, the number and characteristics of these cells can be determined. It has recently been demonstrated that there is a population of memory T lymphocytes with stem cell characteristics, i.e. capable of self-renewal, which accounts for the enduring nature of this memory. An important property of memory T cells is that their metabolic profile is distinct from that of naive T cells. It is marked by the presence of higher mitochondrial energy equipment, enabling these cells to rapidly bring into play energy sources required for activation and division upon stimulation. In vivo experimental studies based on the injection of a single cell have demonstrated the functional diversity of the T lymphocytes generated, and analyzed the modalities of this heterogeneity. An essential notion acquired in recent years concerns the detection of memory T lymphocytes within tissues, close to possible sites of infection: skin, intestine, lungs... This compartmentalization favors adaptation of responses to microorganisms present in a given territory (such as herpes simplex in the skin, rotavirus in the intestine...). This observation has led us to propose a concept of "regional immunity" based on anatomically defined niches.
The persistence of memory T and B lymphocytes over decades has now been demonstrated, despite a relative loss of cells due to senescence and clonal exhaustion. All the work mentioned here contributes to the improvement of vaccine strategies based on the targeting of cellular niches and the precocity of vaccinations.
This lecture was followed by a seminar entitled "B lymphocyte memory", given by Prof. Jean-Claude Weill of Paris-Descartes University, a specialist in B lymphocyte biology. In particular, he discussed the respective roles of long-lived plasma cells and memory B lymphocytes in the persistence and selection of high-affinity antibody production.
