Lymphocytes T CD8+Â : implications dans l'asthme

CD8+ T lymphocytes include several T cell populations with various functional properties: CD8+αβ T cells that produce cytokines (Tc1, Tc2), cytotoxic T cells, CD8+ NKT cells, and CD8+γδ. Their role in asthma has been assessed in a limited number of studies which are reviewed here. Evidence from animal models indicates that conventional CD8+αβ T cells are protective or enhance the immunoallergic immune response. While Tc2 is always an amplifier in immune reactions, the role of Tc1 is still controversial. Cytotoxic T cells, producing perforin and expressing CX3CR1+, are found in excess in asthma, notably during exacerbations. Bronchial infiltration by CD8+ T cells is associated with reduced FEV1 in both asthma and COPD; it is also correlated with asthma mortality. During exacerbations, viruses, allergens, and/or pollutants induce CD8+ lymphocytes that are able to increase asthmatic inflammation, probably non-specifically, via the involvement of these bystander CD8+ cells. The role of the nonconventional CD8+γδ T cells, intermediate between innate and adaptive immunity, is likewise controversial and depends on the models studied. They recognize nonpeptidic antigens and are said to be involved in occupational asthma caused by low molecular weight agents. In conclusion, all the CD8+ T cell populations are implicated in asthmatic inflammation. They are involved in exacerbations of asthma and its severity. As their activation is less sensitive to corticosteroids than CD4+ T cells, targeting CD8+ T cells appears to be an important therapeutic target in severe corticosteroid-dependent asthma.