Activated CD8 T cells bearing MHC class II can interact directly with CD4 T cells

ROMAGNOLI PA; PREMENKO-LANIER MF; ALTMAN JD

Carefree, Arizona

Conferencia; FASEB Summer Research Conference "Biology of the Immune System"; 2008

Federation of American Societies for Experimental Biology (FASEB)

Of all the cells of the murine immune system that require help from CD4 T cells, CD8 T cells are perhaps unique in that they do not appear to express Major Histocompatibility Complex molecules (MHC) class II. As a result, models for how CD4 T cells provide help to CD8 T cells have been proposed that involve a third, MHC class II positive cell as intermediary. Recent data have prompted us to question the dogma that CD8 Tcells can never express MHC class II on their surface and the necessity of an intermediary cell that enable CD4 T cells to provide help for CD8 T cells after the priming has occurred. We propose that activated CD8 T cells can receive help fromCD4 T cells using a direct interaction enabled by the MHC class II on their own surface.Here we show that MHC class II molecules are present on CD8 T cells upon activation and that these molecules are transferred onto them from Antigen Presenting Cells(APC). We also show how that activation of CD8 T cells during an infection leads toMHC class II transfer in vivo, with differing kinetics depending the investigated tissue.Finally, in vitro activated CD8 T cells are able to stimulate experienced CD4 T cells to release IL2, IFN gamma and TNF alpha.These observations suggest a novel window of direct interaction between CD8 andCD4 T cells where there is no need for the presence of an APC once the priming stage has occurred. In addition, this model of interaction envision the possibility of different CD4 T cells impacting into the differentiation program of a CD8 T cell into an effector or memory cell. In consequence, not only can CD8 T cells receive help but also modulation depending on which CD4 T cell subpopulations they are interacting with.