Early activation of TCR alpha gene rearrangement in fetal thymocytes

CTLs: Killers of intracellular bacteria

Many microbial pathogens have evolved a range of capabilities to evade host immune defense mechanisms and to survive and multiply in host cells. The presence of host intracellular bacteria makes it difficult for specific antibodies to function. After the intracellular bacteria escape the attack of the innate immune system, such as phagocytes, they survive in cells, and then adaptive immunity comes into play. Cytotoxic T lymphocytes (CTLs) play an important role in eliminating intracellular bacteria. The regulation of key transcription factors could promote CD4+/CD8+ T cells to acquire cytolytic ability. The TCR-CD3 complex transduces activation signals generated by TCR recognition of antigen and promotes CTLs to generate multiple pathways to kill intracellular bacteria. In this review, the mechanism of CD4/CD8 CTLs differentiation and how CD4/CD8 CTLs kill intracellular bacteria are introduced. In addition, their application and prospects in the treatment of bacterial infections are discussed.

Numerical modelling of the V-J combinations of the T cell receptor TRA/TRD locus

T-Cell antigen Receptor (TR) repertoire is generated through rearrangements of V and J genes encoding α and β chains. The quantification and frequency for every V-J combination during ontogeny and development of the immune system remain to be precisely established. We have addressed this issue by building a model able to account for Vα-Jα gene rearrangements during thymus development of mice. So we developed a numerical model on the whole TRA/TRD locus, based on experimental data, to estimate how Vα and Jα genes become accessible to rearrangements. The progressive opening of the locus to V-J gene recombinations is modeled through windows of accessibility of different sizes and with different speeds of progression. Furthermore, the possibility of successive secondary V-J rearrangements was included in the modelling. The model points out some unbalanced V-J associations resulting from a preferential access to gene rearrangements and from a non-uniform partition of the accessibility of the J genes, depending on their location in the locus. The model shows that 3 to 4 successive rearrangements are sufficient to explain the use of all the V and J genes of the locus. Finally, the model provides information on both the kinetics of rearrangements and frequencies of each V-J associations. The model accounts for the essential features of the observed rearrangements on the TRA/TRD locus and may provide a reference for the repertoire of the V-J combinatorial diversity.

Lymphocytes of the immune system ensure the body defense by the expression of receptors which are specific of targets, termed antigens. Each lymphocyte, deriving from the same original clone, expresses the same unique receptor. To achieve the production of receptors covering the wide variety of antigens, lymphocytes use a specialized genetic mechanism consisting of gene rearrangements. For instance, the genes encoding the receptor of the alpha chain of the T lymphocyte receptor (TRA) spread over a 1500 Kb genetic region which includes around 100 V genes, 60 J genes, and a single C gene. To constitute a functional alpha chain, one of the V and one of the J genes rearrange together to form a single exon. The precise definition of these V-J combinations is essential to understand the repertoire of TRA. We have developed a numerical model simulating all of the V-J combinations of TRA, fitting the available experimental observations obtained from the analysis of TRA in T lymphocytes of the thymus and the blood. Our model gives new insights on the rules controlling the use of V and J genes in providing a dynamic estimation of the total V-J combinations.