Differential peripheral expansion and in vivo antigen reactivity of alpha/beta and gamma/delta T cells emigrating from the early fetal lamb thymus.
The concentrations of different lymphocyte subsets in the blood of lambs which had been thymectomized (Tx) in utero between days 67-75 of fetal gestation were measured at birth and at various intervals during the first year of life. Compared to thymus-intact (Ti) controls, Tx lambs were severely depleted of both alpha/beta and gamma/delta T cells at birth (less than 10% of control levels). The majority of the residual alpha/beta T cells present in Tx lambs at birth were CD4+CD8-. As the Tx lambs aged, the concentration of alpha/beta T cells in blood increased steadily to reach levels around 50% of control values. In contrast, the circulating gamma/delta T cells did not expand in Tx animals and remained barely detectable throughout the observation period, although these cells accounted for 30%-60% of the T cells in the blood of Ti lambs. The expansion of alpha/beta but not gamma/delta T cells was also reflected in changes in the cellular composition of solid lymphoid organs in Tx lambs. B cell numbers were similar in both groups at birth but Tx lambs were persistently B lymphopenic from 3 weeks of age onwards. The alpha/beta T cells that had expanded in Tx lambs responded to stimulation with bacterial antigens in a way that was qualitatively similar to the response in Ti lambs. By contrast, the few gamma/delta T cells in Tx lambs responded abnormally. Our results show that although sheep alpha/beta and gamma/delta T cells are equally thymus dependent during ontogeny, the early fetal thymic emigrants which establish the two T cell lineages in the periphery have strikingly different antigen reactivities and capacities for self-renewal and expansion.
Hein
W R
WR
Basel Institute for Immunology, Switzerland.
Dudler
L
L
Morris
B
B
D000375:Aging / Q000276:immunology*; D000818:Animals; D006967:Hypersensitivity / Q000473:pathology; D007958:Leukocyte Count; D008198:Lymph Nodes / Q000166:cytology; D008221:Lymphoid Tissue / Q000166:cytology; D011948:Receptors, Antigen, T-Cell / Q000032:analysis / Q000096:biosynthesis*; D016693:Receptors, Antigen, T-Cell, alpha-beta; D016692:Receptors, Antigen, T-Cell, gamma-delta; D012756:Sheep / Q000276:immunology*; D012867:Skin / Q000166:cytology; D013154:Spleen / Q000166:cytology; D013601:T-Lymphocytes / Q000276:immunology* / Q000378:metabolism; D013950:Thymus Gland / Q000276:immunology*; D014373:Tuberculin / Q000494:pharmacology
D011948:Receptors, Antigen, T-Cell; D016693:Receptors, Antigen, T-Cell, alpha-beta; D016692:Receptors, Antigen, T-Cell, gamma-delta; D014373:Tuberculin