Human CD1-restricted T cell recognition of lipids from pollens

Plant pollens are an important source of environmental antigens that stimulate allergic responses. In addition to acting as vehicles for foreign protein antigens, they contain lipids that incorporate saturated and unsaturated fatty acids which are necessary in the reproduction of higher plants. The CD1 family of non-polymorphic MHC-related molecules is highly conserved in mammals, and has been shown to present microbial and self lipids to T cells. Here, we provide evidence that pollen lipids may be recognized as antigens by human T cells through a CD1-dependent pathway. Among phospholipids extracted from cypress grains, phosphatidyl-choline and phosphatidyl-ethanolamine were able to stimulate the proliferation of T-cells from cypress-sensitive subjects. Recognition of phospholipids involved multiple cell types, mostly CD4+ TCRalfa-beta+, some CD4-CD8- TCRgamma-delta+, but rarely Valfa24i+ NK-T cells, and required CD1a+ and CD1d+ APC. The responding T cells secreted both IL-4 and interferon-gamma, in some cases IL-10 and TGF-beta and could provide help for IgE production. Responses to pollen phospholipids were maximally evident in blood samples obtained from allergic subjects during pollinating season, uniformly absent in Mycobacterium tuberculosis-exposed health-care workers, but occasionally seen in non-allergic subjects. Finally, allergic, but not normal subjects, displayed circulating specific IgE and cutaneous weal and flare reactions to phospholipids.