Distribution and functional analysis of B-L/Ia-positive cells in the chicken: expression of B-L/Ia antigens on thyroid epithelial cells in spontaneous autoimmune thyroiditis.

The B-L region of the chicken major histocompatibility complex (MHC), the so-called B-locus, corresponds to the murine H-2 I-region. Using alloantibodies and monoclonal antibodies to B-L we analyzed: (a) the tissue distribution of B-L+ cells, (b) the function of B-L+ cells, and (c) the possible role of B-L+ cells in the development of spontaneous autoimmune thyroiditis (SAT) in Obese strain (OS) chickens. The tissue distribution of B-L+ cells in peripheral blood and various lymphoid and nonlymphoid organs corresponds to what is known for mammals. In the bursa of Fabricius most lymphoid cells and the dendritic cells carry the B-L antigen; B-L+ thymic nurse cells (TNC) first appear on day 17 of embryonic life; chickens possess dendritic B-L+ cells in the skin resembling mammalian Langerhans cells; in addition we found that the microglia is unequivocally B-L+. B-L+ peripheral blood lymphocytes (PBL) were separated with a fluorescence-activated cell sorter. Ten percent of unstimulated PBL and 60% of phytohemagglutinin (PHA) stimulated T-cell blasts are B-L+. In graft-vs-host (GvH) assays B-L- cells were identified as the effector cells. These cells respond to PHA and concanavalin A (Con A), but not to pokeweed mitogen (PWM). B-L+ cells cannot be stimulated by Con A and PHA, but respond to PWM. They possess only a very low activity in GvH assays which can be inhibited by anti-T-cell sera. In OS chickens B-L+/non-B/, non-T and B-L+ T (blasts?) cells are found in the "first line" of mononuclear cell infiltration in the thyroid glands. Most interesting, thyroid epithelial cells--which are normally B-L- -become B-L+ in the neighbourhood of B-L+ infiltrating mononuclear cells. This observation may be of significance for autoantigen presentation and perpetuation in autoimmune thyroiditis. Finally, OS thymuses contain significantly less TNC than normal controls.