Ia antigen expressed by keratinocytes can be the molecule of antigen presentation in contact sensitivity.

Immune response-associated (Ia) antigens are important as molecules in antigen recognition by T cells. Keratinocytes can express Ia antigens in many inflammatory dermatoses and by action of gamma interferon (IFN-gamma). A keratinocyte cell line, Pam 212 cells, expressed Ia antigens at maintaining culture. They also expressed Ia antigens under the influence of IFN-gamma. Liposomes carrying molecules from trinitrophenylated-Pam cells did not stimulate lymphnode cells (LCs) of contact sensitivity; however, liposomes carrying a large amount of those molecules stimulated LCs. This stimulation was attributable to contaminated Ia antigens in those molecules. Liposomes with a small amount of those molecules or trinitrophenylated-proteins from Pam cells were prepared. Into them were inserted Ia antigen-rich proteins from Pam cells, spleen cells, IFN-gamma-treated Pam cells, or epidermal cells containing Langerhans cells. Thus prepared liposomes stimulated the LCs significantly. The Ia antigens obtained from IFN-gamma-treated Pam cells worked as well as Ia antigens from epidermal cells that contained Langerhans cells as the molecule of antigen presentation in contact sensitivity.