THE HUMAN THYMUS MICRO-ENVIRONMENT - INVIVO IDENTIFICATION OF THYMIC NURSE CELLS AND OTHER ANTIGENICALLY-DISTINCT SUB-POPULATIONS OF EPITHELIAL-CELLS

Abstract

The human thymus microenvironment was studied to identify subsets of cells that may be responsible for the induction of different aspects of T-lymphocyte differentiation, education and MHC [major histocompatibility complex] restriction. By immunofluorescence on tissue sections and cell suspensions, MHC products (HLA-A, B, C and DR) were throughout the thymus epithelium while human T-cell antigens were absent from all non-lymphoid cells. Thy-1 antigen (expressed on .apprx. 1% pediatric human thymocytes) has a differential expression among thymic epithelial cells, being confined to those in the subcapsular cortex and to thymic nurse cells (TNC). The former represent the site to which thymocyte precursors first migrate upon entering the thymus. The latter are large epithelial cells, located within the cortex, whose plasma membrane totally encloses thymus lymphocytes; these cells are good candidates for the mediators of direct contact (stromal) induced thymocyte maturation.