Regulation of B cell apoptosis

Fcgamma receptor IIB and IIIB polymorphisms and susceptibility to systemic lupus erythematosus and lupus nephritis: a meta-analysis

The aim of this study was to explore whether polymorphisms of the Fcgamma receptors (FcgammaRs) IIB T/I232 and FcgammaRIIIB NA1/NA2, confer susceptibility to systemic lupus erythematosus (SLE) and lupus nephritis (LN). The authors conducted a meta-analysis on associations between the FcgammaRIIB T/I232 and FcgammaRIIIB NA1/NA2 polymorphisms and SLE and LN susceptibility as determined using 1) allele contrast, 2) recessive, 3) dominant models and 4) contrast of homozygotes. A total of 16 separate comparisons were considered, consisting of 2887 SLE patients and 3105 controls. Meta-analysis of the FcgammaRIIB T/I232 polymorphism showed a significant association between the FcgammaRIIB T allele and the risk of developing SLE compared with the FcgammaRIIB I allele (OR = 1.207, 95% CI = 1.061-1.373, P = 0.004). In subjects of Asian descent, a significant association was observed between the FcgammaRIIB T allele and SLE (OR = 1.332, 95% CI 1.138-1.558, P < 0.001). However, in Europeans no such association was found. In contrast, no association was found between SLE or LN and the FcgammaRIIIB NA1/NA2 polymorphism in all subjects, or in European and Asian populations. This meta-analysis shows that the FcgammaRIIB T/I232 polymorphism confers susceptibility to SLE, especially in Asian-derived populations.

Fc receptor genes and the systemic lupus erythematosus diathesis

Fc receptors represent a distinct group of hematopoeitic cell surface glycoproteins that have a characterized role in affecting the efficiency of the mononuclear phagocyte system to clear IgG immune complexes. Functional genetic variations in this family of receptors have been identified as heritable susceptibility factors for SLE and lupus nephritis across diverse populations. In this review, we describe the roles of the classical Fc receptors for IgG (Fc gamma) and non-classical Fc-like receptors (FCR1-FCRL6L), Fc receptors for IgE (Fc epsilon RI) and IgA and IgM (Fc alpha/mu R) in SLE diathesis. The combined effects of these genes on SLE pathogenesis, either via linkage disequilibrium or epistasis with additional genetic or environmental factors, provide a challenge for future investigations. The pursuit of a polygenic SLE-profile that includes longitudinal evaluations of SLE and markers involved in the protean clinical manifestations associated with SLE will facilitate our understanding of the cascade of inflammatory events associated with the diathesis.

Difference in apoptosis induction between surface IgD and IgM

In the classic 'two-signal' model for B cell activation, signal 1 through the antigen receptor plus signal 2 through lymphokine receptors and CD40 leads to proliferation, but signal 1 alone leads to tolerance or anergy. In a protocol designed to deliver signal 1 in vitro with anti-delta without signal 2, purified small dense B cells from untreated mice exposed to any of three monoclonal anti-delta antibodies or to polyclonal anti-delta in vitro showed modest S phase entry at 50 microg/ml. In contrast, at low doses (0.1-0.5 microg/ml) of anti-delta, there was no cell cycle entry at 64 h, but apoptosis was accelerated at 16 h. Polyclonal anti-mu and three monoclonal anti-mus did not show this early apoptosis induction. Anti-CD40 and IL-4 inhibited apoptosis in B cells treated with 0.5 microg/ml anti-delta and increased S phase entry at 10 microg/ml anti-delta. Low-dose anti-delta (but not anti-mu) induced increased B7-2 and class II MHC expression on a subset of B cells, many of which were in apoptosis. Larger transient increases in c-Myc and Egr-1 expression were seen with low-dose anti-delta than with anti-mu, followed by an abrupt fall below baseline, a sequence previously linked to apoptosis. There was no change in Bcl-2, Bcl-x(L) or Bax. These data suggest a functional difference between delta and mu cross-linking on resting spleen B cells. A BCR stimulus sufficient for early activation events, but insufficient for full G1 entry, may lead to apoptosis.

Frequent reversible membrane damage in peripheral blood B cells in human T cell lymphotropic virus type I (HTLV-I)-associated myelopathy/tropical spastic paraparesis (HAM/TSP)

Apoptosis in peripheral blood lymphocyte populations in HTLV-I-infected people in vivo was examined, to study the lymphocyte dynamics in HTLV-I infection. Freshly isolated lymphocytes from 10 non-infected healthy people, eight asymptomatic HTLV-I carriers and 15 patients with HAM/TSP were stained with FITC-labelled annexin V to detect phosphatidylserine (PS) residue exposure at the outer plasma membrane leaflet as an early marker of apoptosis. There was no significant difference in annexin V positivity in CD4+ and CD8+ lymphocytes between non-infected subjects, asymptomatic carriers and HAM/TSP patients, but there was a greatly increased exposure of PS on CD19+ lymphocytes (B cells) detected by FITC-annexin V in 12 out of 15 (80%) HAM/TSP patients, while only two out of eight (25%) asymptomatic carriers and none of the non-infected healthy people showed this aberrant PS exposure on B cells. The intensity of annexin V staining of B cells in HAM/TSP was intermediate, as distinct from the high annexin V staining on advanced apoptotic cells. However, annexin V positivity was decreased when the cells were stained after 24 h of culture, suggesting that the intermediate PS exposure on the B cell in HAM/TSP is not a consequence of an apoptotic process, but rather reflects reversible membrane damage. B cells with PS exposure in vivo might provide a site for coagulation and inflammation, and so contribute to the pathogenesis of HAM/TSP and its complications.

Negative signaling in health and disease

Signal transduction induced by receptors can elicit intracellular biochemical events that either support or inhibit cell activation. Induction of the latter has been termed "negative signaling" and can be triggered by receptors on immune cells that are distinct from activating receptors while other growth-promoting receptors induce both positive and negative signaling events. Here, the biochemistry leading to cell activation or inhibition and induced by receptors on immune cells are reviewed. Furthermore, recent experimental evidence is reviewed that indicates an important contribution of negative signaling to the intracellular survival of infectious pathogens.