Differential expression of CD8 alpha and CD8 beta associated with MHC-restricted and non-MHC-restricted cytolytic effector cells

src-related protein tyrosine kinases and their surface receptors

The CD4-p56lck and CD8-p56lck complexes have served as a paradym for an expanding number of interactions between src-family members (p56lck, p59fyn, p56lyn, p55blk) and surface receptors. These interactions implicate src-related kinases in the regulation of a variety of intracellular events, from lymphokine production and cytotoxicity to the expression of specific nuclear binding proteins. Different molecular mechanisms appear to have evolved to facilitate the receptor-kinase interactions, including the use of N-terminal regions, SH2 regions and kinase domains. Variation exists in stoichiometry, affinity and the nature of signals generated by these complexes in cells. The CD4-p56lck complex differs from receptor-tyrosine kinases in a number of important ways, including mechanisms of kinase domain regulation and recruitment of substrates such as PI 3-kinase. Furthermore, they may have a special affinity for receptor-substrates such as the TcR zeta, MB1/B29 or CD5 receptors, and act to recruit other SH2-carrying proteins, such as ZAP-70 to the receptor complexes. Receptor-src kinase interactions represent the first step in a cascade of intracellular events within the protein-tyrosine kinase/phosphatase cascade.

Transcriptional diversity at the duplicated human CD8 beta loci

In order to understand the structural organization of the human CD8 beta locus, genomic clones containing CD8 beta sequences were isolated and analyzed. Physical linkage of these clones with the CD8 alpha locus using pulsed-field electrophoresis revealed a duplication of the CD8 beta locus. CD8B-1 lies 35 kb upstream from the CD8 alpha locus and contains eight exons, including four alternatively spliced cytoplasmic exons. The CD8B-2 gene contains six exons and is at present unlinked to CD8B-1. Analysis of sequences upstream to the leader exon of the CD8B-1 and CD8B-2 genes revealed a GC-rich promoter which lacks canonical "CCAAT" and "TATA" motifs, but which has sites for multiple transcriptional activators and three additional elements which are conserved in the murine CD8 beta promoter. Seven unique CD8 beta cDNA isoforms were isolated and characterized, which derive from alternative splicing of the transmembrane and/or cytoplasmic exons. Three cDNA are membrane spanning, while the remaining four isoforms lack a transmembrane region and are potentially secreted. These transcripts are differentially expressed in the thymus and in the periphery. Transfection experiments in murine fibroblasts confirmed that the membrane CD8 beta isoforms could be expressed as heterodimers with the CD8 alpha chain. The regulated expression of multiple CD8 beta cytoplasmic isoforms and their potential role in T lymphocyte signal transduction is discussed.

Phenotypic characterization of CD7+, CD3+, and CD8+ lymphocytes from first trimester human decidua using two-color flow cytometry

PROBLEM

There is increasing evidence that decidual lymphocytes play a major role in local interactions at the fetomaternal interface.

METHOD

In this paper we use two-color flow cytometry to delineate the phenotype of lymphocytes obtained from human early decidua by mechanical dispersal technique.

RESULTS

The most abundant decidual lymphocytes expressed CD7, CD38, CD56, and CD2 markers, relatively small proportions of CD3+, CD8+, CD4+, CD16+, CD45RA+, CD11b+, and Leu8+ cells were also present. The vast majority of decidual CD7+ lymphocytes expressed CD38, CD2, and CD56 markers and were CD3-, CD8-, CD16-, and CD57-. Decidual CD3+ lymphocytes were weakly staining for TCR alpha/beta, lacked T-cell receptor (TCR) gamma/delta molecules, and approximately 40% of them expressed HLA-DR. All decidual CD8+ lymphocytes were CD2+ and the majority of them expressed CD38, CD56, and CD7 markers and were CD3- at the same time CD8+CD7- lymphocytes were found in decidua. According to the expression of the CD45RA marker, decidual CD8+ lymphocytes could be divided into two subsets: CD8+CD45RA+CD56+ and CD8+CD45RA-.

CONCLUSIONS

These data clearly demonstrate that decidual lymphocytes display phenotypical features different from those of their counterparts in peripheral blood.

Presence of CD8 alpha-CD8 beta-positive TcR gamma/delta thymocytes in the fetal murine thymus and their in vitro expansion with interleukin-7

Several groups have described that a low percentage of in vitro cultured T cell receptor (TcR) gamma/delta cells express CD8. Contrary to TcR alpha/beta cells, however, CD8 on these TcR gamma/delta cells was shown to be a CD8 alpha homodimer. We describe here that addition of interleukin-7 (IL-7) to a short-term in vitro culture of fetal day 14 thymic lobes in an organ culture system or of fetal day 18 fetal thymocytes in cell suspension yields CD8 beta-positive TcR gamma/delta cells. This is not the result of IL-7-induced expression of CD8 beta on previously CD8 beta-negative cells. It is due to IL-7-induced expansion of CD8 alpha-CD8 beta-positive TcR gamma/delta cells which are shown to be present in the starting fetal thymocyte cell population.