Analysis of structural properties and cellular distribution of avian Ia antigen by using monoclonal antibody to monomorphic determinants.

In this report, we describe the analysis of Ia-like antigens in the chicken by using a monoclonal antibody (CIa-1) reactive with monomorphic determinants of the Ia-like (B-L) antigens. This antibody reacts with determinants on B cells in all avian species tested, but does not detect antigens on lymphocytes of representative mammals, reptiles, and amphibians. In addition to B cells, this antibody defines a subpopulation of the monocyte-macrophage series and reacts with mitogen-activated T cells. Immunochemical analysis indicates that the CIa-1 reactive antigen is a 65,000-dalton glycoprotein consisting of an alpha-chain of 32,000 daltons noncovalently bound to a beta-chain of 27,000 daltons. Under nonreducing conditions, the beta-chain migrates with slightly faster mobility. Two-dimensional gel analysis indicates that the beta-chain is the more heterogeneous of the two chains. Thus, the antigen detected by CIa-1 antibody is similar in cell distribution and structure to the murine Ia antigens and human DR antigens. During in ovo development, Ia+Ig- cells were not found in the yolk sac but were detected in the spleen, mesonephros, and bursa of 9-day embryos. Two populations of Ia+Ig- cells were identified in the bursa: 40 to 60% of the bursacytes, mostly larger cells, exhibited brighter immunofluorescence reactivity than the smaller bursacytes.