MHC II is associated with:-: (A) Antigen presenting cells, (B) Red blood cells, (C) Platelets, (D) Epithelial cells
Answer is A. During antigen recognition, CD4 molecules bind to class II MHC molecules that are displaying antigen (Fig. 6-5), and CD8 molecules bind to class I MHC molecules, and the CD4 or CD8 coreceptor initiates signals that are necessary for activation of the T cells. Because of this requirement for coreceptors, CD4+ helper T cells can recognize and respond to antigen displayed only by class II MHC molecules, whereas CD8+ cytotoxic T cells recognize cell-bound antigens only in association with class I MHC molecules; this segregation is described later. Integrins are adhesion molecules that promote the attachment of T-cells to APCs. To respond, T cells have to recognize not only antigen- MHC complexes but additional signals (CD 28) provided by antigen- presenting cells.