Dysfunction of complement receptors CR3 (CD11b/18) and CR4 (CD11c/18) in pre-eclampsia: a genetic and functional study.

OBJECTIVE: To study genetic variants and their function within genes coding for complement receptors in pre-eclampsia. DESIGN: A case-control study. SETTING: Pre-eclampsia is a common vascular disease of pregnancy. The clearance of placenta-derived material is one of the functions of the complement system in pregnancy. POPULATION: We genotyped 500 women with pre-eclamptic pregnancies and 190 pregnant women without pre-eclampsia, as controls, from the FINNPEC cohort, and 122 women with pre-eclamptic pregnancies and 1905 controls from the national FINRISK cohort. METHODS: The functional consequences of genotypes discovered by targeted exomic sequencing were explored by analysing the binding of the main ligand iC3b to mutated CR3 or CR4, which were transiently expressed on the surface of COS-1 cells. MAIN OUTCOME MEASURES: Allele frequencies were compared between pre-eclamptic pregnancies and controls in genetic studies. The functional consequences of selected variants were measured by binding assays. RESULTS: The most significantly pre-eclampsia-linked CR3 variant M441K (P = 4.27E-4, OR = 1.401, 95% CI = 1.167-1.682) displayed a trend of increased adhesion to iC3b (P = 0.051). The CR4 variant A251T was found to enhance the adhesion of CR4 to iC3b, whereas W48R resulted in a decrease of the binding of CR4 to iC3b. CONCLUSIONS: Results suggest that changes in complement-facilitated phagocytosis are associated with pre-eclampsia. Further studies are needed to ascertain whether aberrant CR3 and CR4 activity leads to altered pro- and anti-inflammatory cytokine responses in individuals carrying the associated variants, and the role of these receptors in pre-eclampsia pathogenesis. TWEETABLE ABSTRACT: Genetic variants of complement receptors CR3 and CR4 have functional consequences that are associated with pre-eclampsia.

The CD11b-integrin (ITGAM) and systemic lupus erythematosus.

Variations at the ITGAM gene, which encodes for the CD11b chain of the Mac-1 (alphaMbeta2; CD11b/CD18; complement receptor-3) integrin, is one of the strongest genetic risk factors for systemic lupus erythematosus (SLE). More specifically, a genetic variant (rs1143679) which results in an arginine to histidine substitution at position 77 in the extracellular portion of the integrin is associated with disease. It has recently been shown that this amino acid substitution results in a dysfunctional integrin, which is deficient in mediating cell adhesion to integrin ligands, phagocytosis and in addition cannot restrict inflammatory cytokine production in macrophages. In this review, we discuss immunological functions of the Mac-1 integrin and how defects in the genetic variant of Mac-1 may relate to SLE development.

An essential role for calmodulin in regulating human T cell aggregation.

After activation of T cells with either CD3 antibodies or phorbol esters, we have found that T cell-cell aggregation, integrin-dependent actin reorganisation and cell spreading are strongly suppressed by any of three structurally different calmodulin antagonists, without any effect on the amount of CD11/CD18 integrin binding to the actin cytoskeleton. However, only T cell receptor-induced, and not phorbol ester-induced, aggregation and cell spreading are prevented by inhibitors of phosphatidylinositide (PI) 3-kinase. These results suggest that PI 3-kinase lies upstream of calmodulin in the signalling pathway leading to T cell aggregation, cell spreading and actin reorganisation and that cell spreading and actin reorganisation are essential for T cell adhesion.

Leukocyte adhesion--an integrated molecular process at the leukocyte plasma membrane.

Leukocyte adhesion is of pivotal functional importance, because most leukocyte functions depend on cell-cell contact. It must be strictly controlled, both at the level of specificity and strength of interaction, and therefore several molecular systems are involved. The most important leukocyte adhesion molecules are the selectins, the leukocyte-specific beta2-integrins and the intercellular adhesion molecules. The selectins induce an initial weak contact between cells, whereas firm adhesion is achieved through integrin intercellular adhesion molecular binding. Although studies during the past twenty years have revealed several important features of leukocyte adhesion much is still poorly understood, and further work dealing with several aspects of adhesion is urgently needed. In this short essay, we review some recent developments in the field.

Leukocyte adhesion--a fundamental process in leukocyte physiology.

Leukocyte adhesion is of pivotal functional importance. The adhesion involves several different adhesion molecules, the most important of which are the leukocyte beta 2-integrins (CD11/CD18), the intercellular adhesion molecules, and the selectins. We and others have extensively studied the specificity and binding sites in the integrins and the intercellular adhesion molecules for their receptors and ligands. The integrins have to become activated to exert their functions but the possible mechanisms of activation remain poorly understood. Importantly, a few novel intercellular adhesion molecules have been recently described, which seem to function only in specific tissues. Furthermore, it is becoming increasingly apparent that changes in integrins and intercellular adhesion molecules are associated with a number of acute and chronic diseases.

The cytoskeletal association of CD11/CD18 leukocyte integrins in phorbol ester-activated cells correlates with CD18 phosphorylation.

Leukocyte adhesion is a regulated process, which involves CD11/CD18 leukocyte integrins. CD11/CD18 acidity may be regulated intracellularly, and the CD18 polypeptide has previously been shown to become phosphorylated on serine and threonine after phorbol ester activation of T cells. Increased adhesiveness is believed to be mediated by regulating the overall avidity of cellular contact. CD11/CD18 integrins have earlier been reported to interact with several cytoskeletal proteins. We have now studied the involvement of the CD18 phosphorylation in cytoskeletal associations. We have investigated the distribution of phosphorylated CD18 between soluble, cytoskeletal and nuclear fractions of T cell detergent lysates. A significant amount of phosphorylated CD18 polypeptides was observed to fraction along with the cytoskeleton, while the majority of the cell surface CD18 molecules remained in the soluble fraction. Putative candidates for this altered cytoskeletal binding of CD11/CD18 were shown to be talin and filamin, which were observed to bind to CD18 cytoplasmic peptides and co-precipitate with CD18. The importance of the CD18 cytoplasmic domain in the regulation of the leukocyte adhesion was further strengthened by inhibition of phorbol ester-induced T cell adhesion with a phosphorylated lipopeptide corresponding to the cytoplasmic portion of the CD18. These results indicate that the induced CD18 phosphorylation and the altered cytoskeletal binding of the phosphorylated integrin complex may contribute to the increased avidity of CD11/CD18-mediated leukocyte adhesion.

Leukocyte integrins and inflammation.

Leukocyte adhesion is of pivotal functional importance. Without adequate adhesion, T lymphocytes and natural killer cells are not cytotoxic, B cells cannot develop into antibody secreting plasma cells, leukocytes do not home into inflamed tissues and myeloid cells are not able to phagocytize or exhibit chemotactic responses. During evolution several leukocyte adhesion molecules have developed belonging to a few molecular families. Among these, the leukocyte-specific integrins (beta 2 integrins, CD11/CD18 molecules) are among the most important. Much progress has taken place during the past few years, and at present we have a considerable knowledge of their structure and function. Inflammation is critically dependent on integrin activity, and its regulation forms the topic of this short review.

The effects of the broadband UVA radiation on myeloid leukemia cells: the possible role of protein kinase C in mediation of UVA-induced effects.

We examined the effects of broadband UVA radiation (320-400 nm) on a rat myeloid leukemia cell line-chloroma (ChL). A Phillips face tanner model HB 171/A was used as a light source. Chloroma were irradiated through a 5 mm thick glass filter that cut off all of the UVB contamination. The irradiances were measured, from 250 to 400 nm, with a well-characterized and calibrated double-grating spectroradiometer Optronic 742. The overall uncertainty of dose evaluation was estimated to be +/-15% (2 sigma). The cells were irradiated with UVA doses of 4 and 8 J/cm2 and cultured thereafter for 24 h. After this period of time, a marked decline up to 50% was observed in cell proliferation in UVA-irradiated ChL cultures. The cell proliferation decline was found to be caused by simultaneously occurring G2/M phase cell cycle arrest and apoptosis in part of the UVA-irradiated ChL population. Concomitantly, with the decline in cell proliferation, an increase was observed in the expression of the major histocompatibility (MHC) class I and II antigens. Because protein kinase C (PKC) is known to regulate cell proliferation, apoptosis and expression of MHC antigens, and because UVA was shown to regulate PKC activity/expression, we therefore examined whether UVA irradiation has any effect on the expression of isozymes of PKC. Western blots revealed that ChL express alpha, beta I, delta, epsilon, eta, and zeta/iota isozymes of PKC and that expression of all isozymes declined 24 h after UVA irradiation (8 J/cm2). Finally, PKC activation in ChL by exposure to phorbol ester caused cell cycle arrest in G1 phase but did not induce apoptosis. This suggests that the previously shown UVA-induced PKC activation in ChL might be responsible for the induction of MHC antigens but the simultaneously observed ChL apoptosis is likely to be mediated by PKC down-regulation. All together, our results suggest that UVA, at irradiance levels that resemble the outdoor exposure, may have profound effects on the immune-related properties of leukocytes. Thus, we speculate that in vivo the immune functions of leukocytes passing through dermal capillaries might be altered by exposure to solar UVA radiation.