Biomedical subjects

M Correia-Neves

Publications and source records attributed to M Correia-Neves.

5 recordsLinked to original sources

PubMed2001

A molecular chart of thymocyte positive selection.

As a new slant on T lymphocyte repertoire selection, we have examined batteries of TCR sequences in thymi from transgenic mice engineered to exhibit limited, focussed TCR diversity. We have tracked the fate of differentiating thymocytes expressing a set of particular TCR through the positive selection process. Subtly different TCR sequences can promote different maturation pathways and commitment choices. Two distinct routes are followed by CD8-lineage cells interacting with MHC class I molecules, via TCR(hi) CD4(+)CD8(+) or CD4(+)CD8(int) intermediates, while CD4-lineage cells mature exclusively via a CD4(+)CD8(int) stage. The CD8-lineage routes are partially exclusive, indicating that the latter cell type is not always preceded by the former. The distribution of sequences also indicates that CD4 / CD8-lineage commitment is not strictly correlated with the class of MHC molecule engaged, and that some mechanism prevents mismatched intermediates from achieving full maturity.

Amino Acid Sequence↗

PubMed2001

The shaping of the T cell repertoire.

By combining a TCRbeta transgene with a TCRalpha minilocus comprised of a single V and two J gene segments, we engineered a mouse line exhibiting ample but focused TCR diversity, restricted to CDR3alpha. Using single-cell PCR and high-throughput sequencing, we have exploited this system to scrutinize T cell repertoire selection and evolution. Some striking observations emerged: (1) thymic selection produces a repertoire that is very "bumpy," with marked overrepresentation of a subset of sequences; (2) MHC class I- and class II-restricted TCRs can be distinguished by minute, single-residue changes in CDR3alpha; and (3) homeostatic expansion and survival in the periphery can markedly remold the postselection repertoire, likely reflecting variability in the potential of cells displaying different TCRs to respond to homeostatic cues.

Animals↗

PubMed1999

Amino acids specifying MHC class preference in TCR V alpha 2 regions.

Some TCR variable regions are preferentially expressed in CD4+ or CD8+ T cells, reflecting a predilection for interacting with MHC class II or class I molecules. The molecular basis for MHC class bias has been studied previously, in particular for V alpha 3 family members, pointing to a dominant role for two amino acid positions in complementary-determining regions (CDRs) 1 and 2. We have evaluated the generality of these findings by examining the MHC class bias of V alpha 2 family members, an attractive system because it shows more variability within the CDR1 and -2, exhibits variation in the framework regions, and includes a member for which the crystal structure has been determined. We find that preferential recognition of MHC class I or II molecules does not always depend on residues at the same positions of CDR1 and -2; rules for one family may be reversed in another. Instead, there are multiple influences exerted by various CDR1/2 positions as well as the CDR3s of both the TCR alpha- and TCR beta-chains.

Amino Acid Substitution↗

PubMed1998

Visualization of CD4/CD8 T cell commitment.

A system to innocuously visualize T cell lineage commitment is described. Using a "knock-in" approach, we have generated mice expressing a beta-galactosidase reporter in place of CD4; expression of beta-galactosidase in these animals appears to be an accurate and early indicator of CD4 gene transcription. We have exploited this knock-in line to trace CD4/CD8 lineage commitment in the thymus, avoiding important pitfalls of past experimental approaches. Our results argue in favor of a selective model of thymocyte commitment, demonstrating a fundamentally symmetrical process: engagement of either class of major histocompatibility complex (MHC) molecule by a differentiating CD4(+)CD8(+) cell can give rise to T cell antigen receptor (TCR)hi thymocytes of either lineage. Key findings include (a) direct demonstration of a substantial number of CD4-committed, receptor/coreceptor-mismatched cells in MHC class II- deficient mice, a critical prediction of the selective model; (b) highly efficient rescue of such "mismatched" intermediates by forced expression of CD8 in a TCR transgenic line, and an explanation of why previous experiments of this nature were less successful-a major past criticism of the selective model; (c) direct demonstration of an analogous, though smaller, population of CD8-committed mismatched intermediates in class I-deficient animals. Finally, we found no evidence of a CD4 default pathway.

Animals↗

PubMed1998

CD4/CD8 lineage commitment: matching fate with competence.

The outcome of positive selection of T lymphocytes is that there is a close match between the lineage adopted by a particular cell (CD4+ or CD8+) and the specificity of the T-cell receptor for the class of Major Histocompatibility Complex molecule recognized. How this match is obtained has been a matter of debate. We review the evidence, from recent and older experiments, that indicates that the process follows a selective logic, rather than an instructive one.

Animals↗