Mouse macrophage beta subunit (CD11b) cDNA for the CR3 complement receptor/Mac-1 antigen

Integrin CD11b negatively regulates BCR signalling to maintain autoreactive B cell tolerance

A variant of the integrin-α-M (CD11b) gene has been linked to the pathogenesis of systemic lupus erythematosus. However, how this genotype results in the lupus phenotype is not fully understood. Here we show that autoreactive B cells lacking CD11b exhibit a hyperproliferative response to B cell receptor (BCR) crosslinking and enhanced survival. In vivo engagement of BCR in CD11b-deficient mice leads to increased autoAb production and kidney Ig deposition. In addition, CD11b-deficient autoreactive B cells have decreased tyrosine phosphorylation including Lyn and CD22 with decreased phosphatase SHP-1 recruitment but increased calcium influx. Results obtained using B cells transfected with the wild type or rs1143679 lupus-associated variant of CD11b suggest that this mutation completely abrogates the regulatory effect of CD11b on BCR signalling. This is through disruption of CD22-CD11b direct binding. These results reveal a previously unrecognized role of CD11b in maintaining autoreactive B cell tolerance.

B-1 cell (CD5+/CD11b+) numbers and nIgM levels are elevated in physically active vs. sedentary rats

Habitual, moderate exercise is associated with improved health, including reductions in illness. These benefits may stem, in part, from immune function improvements. We have previously reported that daily wheel running increases serum and peritoneal natural IgM (nIgM) in pathogen-free Sprague-Dawely rats. B-1 cells, which primarily reside in the peritoneal cavity, produce nIgM in the absence of antigen stimulation. This study examined whether physical activity would also increase B-1 cell numbers in the peritoneal cavity, mesenteric lymph nodes, and spleen. Male, pathogen-free Fischer 344 rats were sedentary (standard cages) or physically active (running wheel access) for 6-7 wk. Peritoneal cavity, mesenteric lymph nodes, and spleen cells were taken, and the number of CD5+/CD11b+ (B-1) cells were measured by using two-color flow cytometry. The results were that physically active animals had increased numbers of CD5+/CD11b+ cells in the peritoneal cavity. In addition, physically active animals had increased serum and peritoneal nIgM, thus replicating our previous observations. These results indicate that voluntary running selectively increases the B-1 cell population, which is most likely responsible for the elevated serum and peritoneal nIgM in active rats. Because B-1 cells are important in host defense, these changes may contribute to the health benefits of exercise.

Antigen-specific B cell memory: expression and replenishment of a novel b220(-) memory b cell compartment

The mechanisms that regulate B cell memory and the rapid recall response to antigen remain poorly defined. This study focuses on the rapid expression of B cell memory upon antigen recall in vivo, and the replenishment of quiescent B cell memory that follows. Based on expression of CD138 and B220, we reveal a unique and major subtype of antigen-specific memory B cells (B220(-)CD138(-)) that are distinct from antibody-secreting B cells (B220(+/)-CD138(+)) and B220(+)CD138(-) memory B cells. These nonsecreting somatically mutated B220(-) memory responders rapidly dominate the splenic response and comprise >95% of antigen-specific memory B cells that migrate to the bone marrow. By day 42 after recall, the predominant quiescent memory B cell population in the spleen (75-85%) and the bone marrow (>95%) expresses the B220(-) phenotype. Upon adoptive transfer, B220(-) memory B cells proliferate to a lesser degree but produce greater amounts of antibody than their B220(+) counterparts. The pattern of cellular differentiation after transfer indicates that B220(-) memory B cells act as stable self-replenishing intermediates that arise from B220(+) memory B cells and produce antibody-secreting cells on rechallenge with antigen. Cell surface phenotype and Ig isotype expression divide the B220(-) compartment into two main subsets with distinct patterns of integrin and coreceptor expression. Thus, we identify new cellular components of B cell memory and propose a model for long-term protective immunity that is regulated by a complex balance of committed memory B cells with subspecialized immune function.

Identification of a beta 2 (CD18) molecule in a teleost species, Ictalurus punctatus Rafinesque

Beta 2, in combination with the alpha subunit, is responsible for tight adhesion of leukocytes, especially neutrophils and macrophages, in areas of inflammation. Although identified in mammalian and avian species; the beta 2 or CD18 molecule has yet to be identified in fish. The present investigation has identified a full-length channel catfish, Ictalurus punctatus, cDNA beta 2 molecule composed of 2.8 kb and a deduced amino acid sequence of 772 amino acids. The catfish molecule has an amino acid homology ranging from 54 to 63% with mouse, bovine, rabbit, human and chicken. The channel catfish molecule retains several characteristics of mammalian beta 2 molecules, such as cysteine-rich repeat regions, N-linked glycosylation sites, and several proposed signal sequences. Expression of the beta 2 molecule on the catfish neutrophil cytoplasmic membranes is increased upon phorbol dibutyrate stimulation of the cells. Based on Western blotting and the immunoprecipitation test, the channel catfish beta 2 molecule has a molecular mass of approximately 95 kD, essentially the same as that for mammalian species. However, two additional molecules, perhaps alpha chains, of unexpected molecular mass appear to co-precipitate in the SPIT with the 95 kD CD18 molecule. These results confirm the existence and expression of a beta 2 gene in channel catfish, a species phylogenetically distant from mammalian species.

Cyclin D1 messenger RNA is induced in microglia rather than neurons following transient forebrain ischaemia

Following 30 min of forebrain ischaemia in the rat, delayed neuronal death occurs in the CA1 sector of the hippocampus within two to three days, whereas neurons in other selectively vulnerable regions, such as the dorsolateral striatum, die within 6-12 h. In this study, we investigated cyclin D1 expression, which codes for a regulatory protein in cell cycle regulation, but it is also induced in sympathetic neurons undergoing programmed cell death. Cyclin D1 messenger RNA could not be detected by in situ hybridization techniques in brains of control rats, but was found at one and two days after ischaemia in regions of the dorsolateral striatum with neuronal degeneration. DNA fragmentation in this region, identified by the terminal transferase biotinylated-UTP nick end labelling (TUNEL) procedure, was observed from 6 h after ischaemia onward. In the hippocampus, increased levels of cyclin D1 messenger RNA were found at two and three days after ischaemia in the striatum pyramidale of the CA1 sector. This expression was associated with the occurrence of neuronal damage and TUNEL-stained neurons. By seven days cyclin D1 messenger RNA was found in hardly any brain structure. There was no temporospatial overlap of cyclin D1 expression with the expression of the immediate-early genes c-fos, c-jun, and mkp-1, a result which is clearly distinct from findings in sympathetic ganglion neurons undergoing programmed cell death. These results do not suggest a role for cyclin D1 in neuronal cell death following transient forebrain ischaemia. The similarity of the cyclin D1 expression profile with that of the microglia-specific CR3 complement receptor beta-subunit messenger RNA, and the results of combined in situ hybridization and microglia-specific immunohistochemistry suggest that microglia are the source of cyclin D1 messenger RNA in the postischaemic brain. Since cyclin D1 codes for a critical regulatory protein for progression of the G0 to G1 phase in the cell cycle and we did not observe prominent occurrence of DNA fragmentation in microglial cells in the hippocampus at time points when cyclin D1 messenger RNA was found, we suggest that cyclin D1 induction is involved in the onset of microglial cell proliferation.

The purification and characterization of fetal liver hematopoietic stem cells

Thy-1loSca-1+Lin-Mac-1+CD4- cells have been isolated from the livers of C57BL-Thy-1.1 fetuses. This population appears to be an essentially pure population of hematopoietic stem cells (HSC), in that injection of only six cells into lethally irradiated adult recipients yields a limit dilution frequency of donor cell-reconstituted mice. Sixty-seven to 77% of clones in this population exhibit long-term multilineage progenitor activity. This population appears to include all long-term multilineage reconstituting progenitors in the fetal liver. A high proportion of cells are in cycle, and the absolute number of cells in this population doubles daily in the fetal liver until 14.5 days postcoitum. At 15.5 days postcoitum, the frequency of this population falls dramatically. Long-term reconstituting HSC clones from the fetal liver give rise to higher levels of reconstitution in lethally irradiated mice than long-term reconstituting HSC from the bone marrow. The precise phenotypic and functional characteristics of HSC vary according to tissue and time during ontogeny.

The gene organisation of the human beta 2 integrin subunit (CD18)

We have studied the gene of the human beta 2 integrin subunit (CD18) and found it to be organised into 16 exons spanning a region of about 40 kb. All exon/intron boundaries conform to the GT/AG splicing consensus. The exons coding for the cysteine-rich region, which has been postulated to consist of 3 or 4 repeating elements, are not organised correspondingly. Transcription of the gene initiates from multiple sites which may be due to the absence of an upstream TATA box. The polyadenylation site is also heterogeneous. Five different sites were identified over a stretch of 10 bases.