title: Gamma/delta T cells express a unique surface molecule appearing late during thymic development.
abstract: The vast majority of T cells in man and mouse use the alpha/beta form of T cell receptor (TcR), and express either CD4 or CD8, whereas the small subset of gamma/delta T cells are usually CD4-CD8-. In contrast to man and mouse, the gamma/delta subset in sheep, defined here using an anti-gamma/delta monoclonal antibody (mAb), comprises 30%-60% of T cells. We show that gamma/delta T cells in sheep express a unique surface molecule termed T19 which is 215 kDa in size and unrelated to either CD45 or the TcR. The T19 molecule was expressed at a distinct stage during gamma/delta T cell ontogeny within the thymus, since gamma/delta thymocytes which appeared early in fetal ontogeny were T19- and also major histocompatibility complex (MHC) class I- and localized almost exclusively to the outer cortex and cortex of the thymus. "Mature-type" gamma/delta thymocytes which emerged late in thymic development were T19+ and MHC class I+ and localized predominantly to the thymic medulla. The sequence of events indicated that these cells were most likely derived from the early gamma/delta thymocytes. These medullary gamma/delta thymocytes showed a very distinctive association with Hassall's corpuscles, suggesting a role for these structures in gamma/delta thymocyte maturation. In the periphery, T19 was expressed exclusively within the gamma/delta T cell subset, however some gamma/delta T cells were T19-. In particular, a large proportion of gamma/delta T cells within intestinal epithelium lacked T19, indicating a correlation between T19 expression and either function or homing patterns of gamma/delta T cells. Both T19+ and T19- gamma/delta T cells were CD2-, and expressed low levels of LFA-1 and CD5. In addition, gamma/delta T cells recirculated differently from other T cells, and appeared not to enter mesenteric lymph nodes at all from the blood. We propose that T19 is a maturation marker for gamma/delta T cells. In addition, the exclusive expression of T19 by gamma/delta T cells indicates that this molecule most likely serves a fundamental role in the interactions and function of gamma/delta T cells.
authors.affiliation: Basel Institute for Immunology, Switzerland.
authors.forename: C R
authors.initials: CR
authors.lastname: Mackay
authors.forename: M F
authors.initials: MF
authors.lastname: Beya
authors.forename: P
authors.initials: P
authors.lastname: Matzinger
mesh_terms: D000818:Animals; D000945:Antigens, Differentiation, T-Lymphocyte / Q000032:analysis*; D007124:Immunoenzyme Techniques; D007422:Intestines / Q000276:immunology; D008970:Molecular Weight; D011948:Receptors, Antigen, T-Cell / Q000502:physiology; D016692:Receptors, Antigen, T-Cell, gamma-delta; D012756:Sheep; D013601:T-Lymphocytes / Q000145:classification / Q000166:cytology / Q000276:immunology*; D013950:Thymus Gland / Q000166:cytology* / Q000276:immunology; D014018:Tissue Distribution
chemical_list: D000945:Antigens, Differentiation, T-Lymphocyte; D011948:Receptors, Antigen, T-Cell; D016692:Receptors, Antigen, T-Cell, gamma-delta