Faculty Bibliography

A number of recent reports have established that oligoclonality and/or clonal expansion is a common feature of the CD8+ T cell population. Oligoclonal expansion has also been observed in bone marrow transplant recipients and rheumatoid arthritis patients, disease states in which CD57+CD8+ T cells are occasionally elevated. In this study we have compared the TCR repertoire of the CD57+ and CD57- subsets of CD8+ T cells in normal persons by using three-color FACS analysis with a panel of 16 mAbs specific for TCR V segments. The CD57 surface marker was highly variable in frequency but generally present on a minority of CD8+CD3+ T cells (mean 16.3%, SD 12.7) in a group of 41 normal volunteers. Dramatic oligoclonal expansion was present in the CD57+CD8+ T cell population in 15 of 41 (37%) of our study population and thus is a characteristic feature of the normal immune system. No such prominent oligoclonal expansions were observed in the CD57-CD8+ subset, although preliminary experiments suggest that oligoclonality per se is occasionally present at a lower frequency in CD57- cells. The reasons for this persistent accumulation of oligoclonal CD8+CD57+ T cells and their function in immune homeostasis are unclear

The CD79a (Ig-alpha/mb-1) and CD79b (Ig-beta/B29) molecules form a membrane heterodimer that is non-covalently associated with surface membrane immunoglobulin and is the major signaling component of the B cell antigen receptor complex. We have defined variant RNA transcripts for both CD79a (Ig-alpha/mb-1) and CD79b (Ig-beta/B29) which appear to arise by alternative splicing. These splice variants are predicted to encode truncated forms of these molecules that result in the deletion of the entire extracellular Ig-like domain of CD79b and of a major portion of the extracellular domain of CD79a. The presence of these short transcripts in a variety of human B cells and B cell lines was established by an RNAse protection assay. The definition of these variant transcripts provides a basis for a continuing effort to define variant protein products of CD79a and CD79b and examine their role in B cell physiology

BACKGROUND: Monozygotic (MZ) twinning is a poorly understood phenomenon that may result in subtle biologic differences between twins, despite their identical inheritance. These differences may in part account for discordant expression of disease in MZ twin pairs. Due to their stochastic nature, differences in X chromosome inactivation patterns are one source of such variation in female MZ twins. MATERIALS AND METHODS: We investigated X chromosome inactivation patterns in the blood of 41 MZ twin pairs based on methylation of the androgen receptor gene using a Hpa II-PCR assay. Twenty-six female MZ twin pairs with autoimmune disease (rheumatoid arthritis or multiple sclerosis) were studied. In addition, we studied 15 newborn female MZ twin pairs who were characterized at birth with respect to the anatomy of chorionic membranes (dichorionic versus monochorionic). RESULTS: We found a strong correlation between dichorionic fetal anatomy and differences in X chromosome inactivation patterns between members of an MZ twin pair. In contrast, all monochorionic twin pairs had closely correlated patterns of X chromosome inactivation. X chromosome inactivation patterns did not distinguish between MZ twin pairs who were concordant or discordant for autoimmune disease. CONCLUSIONS: The highly similar patterns of X chromosome inactivation among monochorionic twin pairs may result from their shared placental blood supply during intrauterine life. Alternatively, these patterns may indicate that X chromosome inactivation occurs before the twinning event in this anatomic subgroup of MZ twins. The data further suggest that these factors do not make a major contribution to the high discordance rates for autoimmune disease in MZ twin pairs

We determined the complete genomic sequence of the human CD79b (Ig beta/B29) gene. The CD79b gene product is associated with the membrane immunoglobulin signaling complex which is composed of immunoglobulin (Ig) itself, associated in a noncovalent fashion with CD79b and a second polypeptide chain, CD79a (Ig alpha/mb1). The sequence and exon/intron organization of the human and mouse CD79b genes are highly similar. The gene organization suggests that some variant forms of CD79b may arise by virtue of alternative splicing of mRNA. In addition, a number of conserved regulatory sequences commonly found in Ig genes are present in sequences which flank the human CD79b gene. Some of these sequences are distinct from those found in the CD79a promoter. These differences may explain why transcription of CD79b, but not CD79a, is observed in plasma cells. A new Taq 1 restriction fragment length polymorphism is described that is not associated with any structural polymorphisms of the expressed CD79b polypeptide

The germline DNA sequence of the human CD79 alpha (Ig-alpha/mb-1) gene was determined by polymerase chain reaction sequencing of a cosmid clone derived from an arrayed human chromosome 19 library. The CD79 alpha gene was localized to chromosome 19q13.2; this localization places the gene within the CEA-like gene cluster with the following gene order: -CEA-CGM1-CD79 alpha-RPS11-ATP1A3-BGP-CGM9-. The genomic organization of the human CD79 alpha gene resembles the mouse counterpart with five exons interrupted by four introns. Computer analyses suggest the presence of transcription regulatory elements known to be important in the regulation of mouse CD79 alpha (AP-1, EBF, AP-2, MUF2, and SP-1 sites), as well as elements not found in the mouse gene (an NK-kappa B binding site and a series of E-box motifs). Similar to the mouse gene, the 5' flanking region of human CD79 alpha lacks a TATA box; however, unlike mouse CD79 alpha, a classical octamer motif could not be identified in the human gene. Finally, a new Rsa I restriction fragment length polymorphism was defined in the non-coding regions of the human gene

Structural models for the TCR alpha/beta predict that the CDR1, CDR2, and CDR3 loops of both the alpha- and beta-chains contribute to specific interactions with the Ag/MHC complex. The CDR3 loops are constructed by joining events involving the V-(D)-J segments, and thus may vary in both sequence and length. We have developed a polymerase chain reaction assay to assess the length variation of the CDR3 loop in TCR derived from seven V beta segment families (V beta 2, V beta 3, V beta 4, V beta 9, V beta 14, V beta 16, and V beta 17). Peripheral blood T cells from 10 normal adults as well as five cord blood samples were studied. CD4+ and CD8+ T cells were analyzed separately. We observed extreme predominance of particular CDR3 lengths in half of the normal adults. These TCR were shown to be clonal by direct sequence analysis. This clonal dominance was found in the CD8+, CD45RO+ T cell population, and was observed in various V segment families. These patterns of TCR clonality were persistent over many months of observation in some individuals. In one subject, the new appearance of a predominant clone was associated with a booster vaccination for hepatitis B. These studies reveal a surprising degree of oligoclonality in the CD8+ cells of normal subjects which may be due to both environmental and genetic factors; the functional significance of persistent clonal dominance in the CD8 compartment remains to be determined