INTRATHYMIC DISTRIBUTION OF THE 2 AVIAN THYMIC PARVALBUMINS

Although parvalbumins are generally viewed as intracellular Ca2+ buffe rs/transporters, avian species express two thymus-specific isoforms th at may play alternative biological roles. These proteins, known as avi an thymic hormone (ATH) and chicken parval-bumin 3 (CPV3), are conject ured to influence thymopoiesis. In this paper, we compare their intrat hymic distributions. Isoform-specific monoclonal antibodies against AT H and CPV3 were labeled with fluorescein and Cy5, respectively, and th en used to probe paraffin sections of chicken thymus tissue. Confocal microscopy of the stained sections reveals that ATH and CPV3 are both confined to the thymic cortex and that they are frequently coexpressed by a subset of epithelial cells. However, their expression patterns a re not completely superimposible. Cortical epithelial cells are also o bserved that stain for just one of the two avian parvalbumin isoforms, albeit at lower frequency. Significantly, a subset of cortical thymoc ytes exhibits peripheral staining for one or both of the proteins. Thi s result may imply the existence of plasma membrane receptors for the two proteins on select T-cell precursors. Alternatively, it may signal low level expression of the thymic parvalbumins by the thymocyte popu lation. (C) 1995 Academic Press, Inc.