Expression of Ia antigens on freshly dissociated mouse thyroid follicles demonstrated by immunofluorescence

Iak antigens were detected by indirect immunofluorescence on CBA mouse thyroid follicles. Isolated thyroid follicles, free of lymphocyte contamination, were obtained by collagenase treatment and mechanical disruption; they were then cytocentrifuged on glass slides. This material was incubated with polyclonal or monoclonal anti Iak antibodies followed by FITC-conjugated F(ab')2. Subsequent microscopic observations of these open thyroid follicles revealed that Iak antigens were spontaneously expressed. Labelling was distributed preferentially on the thyrocyte cell surface and, to a lesser extent, on intracellular organelles. Conversely, nuclei were never stained. In some cases, labelling was mottled. Ia antigens may have been previously unobserved because, beside autoimmune disorders they are present in such small amounts that detection is very difficult. The fact that Ia expression is independent of morphological signs of spontaneous autoimmune thyroiditis (particularly, lymphocyte infiltration of follicles), raises the problem of correlation between the autoimmune disorders and Ia expression.