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Hector Molina

Publications and source records attributed to Hector Molina.

12 recordsLinked to original sources
PubMed2005

Several genes contribute to the production of autoreactive B and T cells in the murine lupus susceptibility locus Sle1c.

The systemic lupus erythematosus 1 (Sle1) locus mediates the loss of tolerance to nuclear Ags in the NZM2410 mouse model of lupus through intrinsic defects in both B and T cells. Congenic analysis has shown that Sle1 corresponds to at least three genetic loci, Sle1a, Sle1b, and Sle1c. Telomeric Sle1c is associated with abnormal B cell responses to subthreshold stimulation with anti-IgM and C3d and with decreased T-dependent humoral immune responses. We have proposed that these phenotypes resulted from polymorphisms in the C3 complement receptor Cr2 gene. We have also found that Sle1c was associated with the production of histone-specific autoreactive CD4(+) T cells, which correlated with higher activation and proliferative responses, and a reduction in the CD4(+)CD25(+)CD62L(+)forkhead/winged helix transcription factor gene (Foxp3(+)) compartment. In this study we showed, using congenic recombinants, that the decreased humoral immune response and impaired GC formation map to the NZM2410 Cr2 allele. A chronic graft-vs-host disease model also showed that Sle1c produces significantly more autoreactive B cells than B6 controls, and that this phenotype maps to two regions excluding the Cr2 gene. Mixed bone marrow chimera demonstrated that the increased activation, proliferative response, and reduced regulatory T cell compartment were intrinsic to Sle1c-expressing CD4(+) T cells. These phenotypes mapped to the same two loci identified with the chronic graft-vs-host disease model, excluding the Cr2 region. Overall, these results show that Sle1c results in the production of autoreactive B and T cells through the expression of three different genes, one of which is consistent with Cr2, based on the phenotypes of the Cr2-deficient mice, and the other two corresponding to as yet unidentified genes.

Animals↗
PubMed2004

Complement and immunity.

Our body is in constant interaction with the environment. Some of the interactions involve the recognition and disposal of foreign substances that may harm the delicate balance between health and disease. The foreign elements, or antigens, include infectious organisms and lifeless macromolecules. The ability of the body to recognize what is dangerous and what is inconsequential, and to refrain from damaging what is perceived as self, are the main functions of the immune system. One important component of the innate immune response is the complement system. This article describes the different mechanisms of how complement is activated and the consequence of this activation, followed by a characterization of the complement's role in inflammation and autoimmunity, and the therapeutic considerations emanating from these studies.

Animals↗
PubMed2003

A novel mechanism of complement-independent clearance of red cells deficient in glycosyl phosphatidylinositol-linked proteins.

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired hemolytic anemia characterized by the increased sensitivity of red blood cells (RBCs) to complement, leading to intravascular hemolysis and hemoglobinuria. PNH is due to the expansion of a cell clone that has acquired a mutation in the PIGA gene. Mice with targeted Piga gene inactivation genetically mimic the human disease and have phosphatidylinositol glycan class A-negative (PIGA-) RBCs with a reduced half-life in circulation. Although PIGA-RBCs are hypersensitive to complement in vitro, their complement sensitivity in vivo is barely detectable. Here we show that the shortened survival of PIGA- RBCs is independent of complement either by using inhibitory C5 antibodies or by transfusion into C5-, C4-, C3-, or factor B-deficient mice. Splenectomy or high-dose cortisone treatment had no effect on the shorter survival of PIGA- RBCs. However, treatment with liposome-encapsulated clodronate, an agent that depletes macrophages in vivo, normalized the half-life of PIGA- RBCs. This indicates that the shortened survival of PIGA- RBCs is due to a novel pathway of PIGA- RBC clearance that is mediated by macrophages, but occurs independently of complement. Future investigations will show whether this novel pathway of PIGA- RBC destruction identified in mice may also operate in patients with PNH.

Anemia, Hemolytic↗
PubMed2003

Complement component 3 is required for optimal expansion of CD8 T cells during a systemic viral infection.

In addition to its established role in innate immune mechanisms, complement component C3 is also of critical importance in B cell activation and T cell-dependent Ab responses. In this study, we have examined the requirement for C3 in the generation of primary CD8 T cell responses to an acute systemic viral infection. We compared Ag-specific CD8 T cell responses to lymphocytic choriomeningitis virus (LCMV) between wild-type (+/+) and C3-deficient (C3(-/-)) mice on both 129/B6 and B6 backgrounds. These studies revealed that C3 activity is required for optimal expansion of LCMV-specific effector CD8 T cells in an epitope-dependent fashion, which is influenced by the genetic background of the mice. Studies in complement receptor 1/2 (CR1/CR2)-deficient mice showed that regulation of LCMV-specific CD8 T cell responses by C3 is not dependent upon CR1/CR2. These findings may have implications in vaccine development, therapy of autoimmune diseases, and prevention of graft rejection.

Acute Disease↗
PubMed2003

Tolerance is dependent on complement C3 fragment iC3b binding to antigen-presenting cells.

Systemic tolerance can be induced by the introduction of antigen into an immune-privileged site. Here we investigated the role of complement in the induction of tolerance after intraocular injection. We found that the development of antigen-specific tolerance is dependent on a complement activation product. The ligation of the complement C3 activation product iC3b to complement receptor type 3 (the iC3b receptor) on antigen-presenting cells resulted in the sequential production of transforming growth factor-beta2 and interleukin-10, which is essential for the induction of tolerance. These observations may extend to the development of both neonatal tolerance and other forms of acquired tolerance.

Animals↗
PubMed2003

Hepatic overexpression of caveolins increases bile salt secretion in mice.

Caveolins are cholesterol-binding proteins involved in the regulation of several intracellular processes, including cholesterol transport. Because hepatocytes express caveolin-1 and caveolin-2, these proteins might modulate hepatic lipid metabolism and biliary lipid secretion. Our aim was to investigate the potential physiologic role of caveolins in hepatic cholesterol and bile salt (BS) metabolism and transport using adenoviral gene transfer. C57BL/6 mice were infected with recombinant human caveolin-1 and caveolin-2 adenoviruses. Mice infected with adenovirus lacking the transgene were used as controls. Hepatic caveolin expression was evaluated by immunochemical methods. Reverse-transcription polymerase chain reaction (RT-PCR) and immunoblotting were used to assess messenger RNA (mRNA) levels and protein mass of BS transporters (sodium taurocholate cotransporting polypeptide [Ntcp] and bile salt export pump [Bsep]). Serum, liver, biliary, and fecal biochemical determinations and BS maximal secretory rate (SRm) were performed by standard methods. Ad.Cav-1- and Ad.Cav-2-infected mice exhibited a 10- and 7-fold increase in hepatic caveolin-1 and caveolin-2 protein expression, respectively. Caveolin-1-overexpressing mice had a significant increase in plasma high-density lipoprotein (HDL) cholesterol and hepatic free cholesterol content, whereas total plasma cholesterol and triglyceride levels remained unchanged. Hepatic caveolin-1 and/or caveolin-2 overexpression significantly increased bile flow and secretion of all biliary lipids. Caveolin-1-overexpressing mice showed a 2.5-fold increase in taurocholate (TC) SRm, indicating increased canalicular BS transport capacity. BS pool size and fecal BS excretion remained within the normal range in mice with Cav-1 overexpression. No changes were seen in the protein mass of BS transporters Ntcp and Bsep. In conclusion, our findings indicate that caveolins may play an important role in regulating hepatic BS and cholesterol metabolism.

Adenoviridae↗
PubMed2003

Negligible role of antibodies and C5 in pregnancy loss associated exclusively with C3-dependent mechanisms through complement alternative pathway.

Factors involved in pregnancy failure due to abnormal fetomaternal tolerance are poorly understood. Here we describe distinct defects in placenta formation and subsequent pregnancy loss solely dependent on the activation of the complement alternative pathway and the effector mechanisms provided by the maternal C3. Surprisingly, this effect is independent of other complement activation pathways and of the effector mechanisms provided by other complement components. These findings provide significant insight into the role of the innate immune system in human pregnancy failure, a frequent clinical outcome.

Abortion, Spontaneous↗
PubMed2002

Complement-mediated clearance of erythrocytes: mechanism and delineation of the regulatory roles of Crry and DAF. Decay-accelerating factor.

The role of complement in the pathogenesis of autoimmune hemolytic anemia (AIHA) has been controversial and may depend on a number of factors, including the affinity and isotype of the pathogenic antibodies involved. We have recently shown that mouse erythrocytes deficient in the membrane C3 regulatory protein, complement receptor 1-related gene/protein y (Crry), but not decay-accelerating factor (DAF), were spontaneously eliminated in vivo by complement. Here, by generating a mouse deficient in both DAF and Crry, we further delineated the roles of Crry and DAF in regulating alternative and classical pathway C3 activation. By using immunoglobulin-, Fcgamma receptor (FcgammaR)-, C3-, C4-, and C5-deficient mice, we also determined the mechanism by which membrane C3 regulator-deficient erythrocytes are cleared from the circulation. Finally, we evaluated the relative importance of the Fc receptor versus the complement pathway in disposing antibody-opsonized DAF/Crry-deficient erythrocytes. We conclude that (1) Crry plays a more dominant role than DAF in regulating the alternative pathway of complement, whereas DAF and Crry are equally effective in preventing antibody-induced runaway complement activation on mouse erythrocytes; (2) DAF/Crry-deficient erythrocytes are eliminated by the alternative pathway of complement via complement receptor-mediated erythrophagocytosis in the spleen; and (3) when opsonized with an immunoglobulin G2a (IgG2a) autoantibody, Crry/DAF-deficient erythrocytes are eliminated more rapidly by complement than by the Fc receptor pathway. These results shed new light on the relative activities of Crry and DAF and underscore the critical roles of membrane C3 regulators in preventing spontaneous and antibody-induced erythrocyte damage in vivo.

Agammaglobulinemia↗
PubMed2002

Crry, but not CD59 and DAF, is indispensable for murine erythrocyte protection in vivo from spontaneous complement attack.

Decay-accelerating factor (DAF) and CD59 are 2 glycosylphosphatidylinositol-anchored membrane proteins that inhibit complement activation at the C3 and C5b-9 step, respectively. CD59 is considered critical for protecting erythrocytes from spontaneous complement attack, as deficiency of CD59 or CD59/DAF, but not of DAF alone, on human erythrocytes renders them sensitive to complement lysis in paroxysmal nocturnal hemoglobinuria syndrome. To evaluate the relative roles of CD59 and DAF in vivo, we have generated and studied a CD59 knockout and a CD59/DAF double-knockout mouse. CD59-deficient and CD59/DAF-double-deficient mouse erythrocytes were highly sensitive to antibody-induced complement lysis in vitro, yet neither CD59 knockout nor CD59/DAF double-knockout mouse developed spontaneous hemolytic anemia. Consistent with the latter observation, erythrocytes from the 2 strains of mutant mice were shown to have a normal lifespan in vivo. In contrast, mouse erythrocytes deficient in complement receptor 1 (CR1)-related gene y (Crry), a membrane C3 inhibitor with DAF and membrane cofactor protein activities, were rapidly eliminated from the circulation by a complement-dependent mechanism. Compared with DAF-deficient erythrocytes, Crry-deficient erythrocytes incurred higher levels of spontaneous C3 deposition in vivo. These findings demonstrate that CD59 and DAF are not indispensable on murine erythrocytes. Rather, effective C3 regulation on the cell surface, provided by Crry rather than DAF, is necessary for mouse erythrocytes to resist spontaneous complement attack. Our results raise the possibility that proper control of C3 activation may also be critical on human erythrocytes, where CR1 but not DAF could be the principal regulator of spontaneous C3 activation.

Animals↗
PubMed2002

Complement C3 activation is required for antiphospholipid antibody-induced fetal loss.

The antiphospholipid syndrome (APS) is characterized by recurrent fetal loss, vascular thrombosis, and thrombocytopenia occurring in the presence of antiphospholipid (aPL) antibodies. The pathogenesis of fetal loss and tissue injury in APS is incompletely understood, but is thought to involve platelet and endothelial cell activation as well as procoagulant effects of aPL antibodies acting directly on clotting pathway components. Recent studies have shown that uncontrolled complement activation in the placenta leads to fetal death in utero. We hypothesized that aPL antibodies activate complement in the placenta, generating split products that mediate placental injury and lead to fetal loss and growth retardation. To test this hypothesis, we used a murine model of APS in which pregnant mice are injected with human IgG containing aPL antibodies. We found that inhibition of the complement cascade in vivo, using the C3 convertase inhibitor complement receptor 1-related gene/protein y (Crry)-Ig, blocks fetal loss and growth retardation. Furthermore, mice deficient in complement C3 were resistant to fetal injury induced by aPL antibodies. While antigenic epitopes recognized by aPL antibodies are important in the pathogenesis of APS, our data show that in vivo complement activation is required for aPL antibody-induced fetal loss and growth retardation.

Animals↗
PubMed2002

Update on complement in the pathogenesis of systemic lupus erythematosus.

Complement is involved in inflammation and in the optimization of adaptive responses. Abnormalities in the complement system have been associated with autoimmunity, especially systemic lupus erythematosus. A paradoxic relation exits between complement and lupus. Complement-mediated tissue damage is accepted as a mechanism in disease pathophysiology. Conversely, complement exerts a protective effect in disease development. The theoretic framework explaining this protective influence involves the adequate disposal of apoptotic material by classic pathway components. Inadequate clearance of apoptotic material may evoke a proinflammatory autoimmune response. This conceptual model is substantiated by studies indicating that complement receptor genes are within major susceptibility loci of systemic lupus erythematosus, that functional and structural abnormalities in these receptors are found in lupus mouse models, and that genetic polymorphism of lectin pathway genes correlates with increased risk of disease development. Finally, new diagnostic and therapeutic modalities based on complement regulation have been described in the past year.

Animals↗