T-cells precursors

Haynes, B.F., et al. Early events in human T cell ontogeny. Phenotypic characterization and immunohistologic localization of T cell precursors in early human fetal tissues, J. Exp. M.d., 168, 1061, 1988. 

Also termed 7-chemokines, C Chemokines are composed of only two cysteines one on the N-terminus and the other a downstream cysteine. There are two chemokines in this group, lymphotactin-a (XCL1) and lymphotactin-(3 (XCL2). Their function is the attraction of T-cell precursors to the thymus. 

H13. Haynes, B. F., Denning, S. M., Singer, K. H., and Kurtzberg, J., Ontogeny of T-cell precursors A model for the initial stages of human T-cell development. Immunol. Today 10, 87-91 (1989). 

Transforming growth factor-beta and IL-4 cause helper T cell precursors to develop into distinct effector helper cells that differ in lymphokine secretion pattern and cell surface phenotype. J. Immunol. 147, 2991-3000. 

In addition to inducing T cell antigens, TF5, TP3, TP4, and Taj have been shovra to induce the expression of TdT in normal mouse bone marrow cells. Of particular interest are studies demonstrating that only 50% of Lyt-1,2,3 induced cells are TdT" ", suggesting the existence of TdT and TdT+ T-cell precursors in bone marrow, the latter of which might give rise to a medullary thymocyte population (Goldschneider et al., 1981). 

The utilization of peripheral blood lymphoid cells as target cells for evaluating the immunomodulatory effects of thymic factors is based on the assumption that circulating thymic hormones continue to interact with mature T cells and play a role in the maintenance of thymic-dependent immunity. Because of the ease in isolating peripheral blood lymphocytes from venipuncture specimens, this population of cells has frequently been employed experimentally. It must be emphasized, however, that when unffactionated peripheral blood lymphocytes are used as target cells, the predominant cells present are mature T lymphocytes. Thus, when unfiactionated peripheral blood lymphocytes are used as targets, it would be difficult to discern any effects on T cell precursors since they would make up, at best, only a very minor component of the lymphoid population being studied. 

B9. Barcena, A., Toribio, M. L., Pezzi, L., and Martinez, C. A role for interIeukin-4 in the differentiation of mature T cell receptor gamma/delta -r cells from human intrathymic T cell precursors. J. Exp. Med. 172, 439 46 (1990). 

Russell CA, Vindelov LL. Optimization and comparison of the MTT assay and the 3H-TdR assay for the detection of IL-2 in helper T cell precursor assays. J Immunol Methods 1998 217 165-175. 

T-cell lymphoma is a clonal proliferation of neoplastic cells originated from different stages of T-lymphocytes. Thymic and prethymic T-cell lymphomas derive from the early T-cell precursors vhereas peripheral T-cell lymphomas from more mature T-lymphocytes. T-lymphocytes are characterized by the expression of T-cell receptors (TCR) on the membrane surface. These receptors are essential for the recognition of antigens and different Immunologic reactions. The T-cell receptor (TCR) is a heteromer with two subtypes ... 

In fact, however, it must be pointed out that as yet the precise cellular locus of action of the antigen-specific T cell factor of Taussig and colleagues has not been defined and must be considered to be open at the moment. The fact that the latter factor works with bone marrow cells does not mean that its effect is directly on B cells since bone marrow is known to contain variable numbers of T cells and T cell precursors. Thus, the effect of the factor could be to facilitate maturation of precursor T cells to functional helper cells which would in turn cooperate with B cells. Moreover, it is possible that if the factor does indeed work directly on B cells, that this may be peculiar to immature B cells of bone marrow and not as much so in the case of more mature peripheral B lymphocytes. Further analysis is required to distinguish between these possibilities. 

The current hematopoietic model also proposes the existence of a lymphoid-restricted CLP, which can be separated from the CMP based on expression of the IL-7 receptor. The progeny of the CLP develop into B cell precursors that remain in the bone marrow or T cell precursors that migrate to the thymus. Although mature lymphocytes are generally quiescent, specific memory T and B cells can be reactivated by their cognate antigen to proliferate, expand, and fight infection. 

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