Complement receptors type 1 (CR1, CD35) and 2 (CR2, CD21) cooperate in the binding of hydrolyzed complement factor 3 (C3i) to human B lymphocytes

The C3b-binding receptor, CR1/CD35, supports CR2/CD21-mediated activation of complement by human B lymphocytes, possibly by associating with CR2 to promote or stabilize the binding of hydrolyzed C3 (C3i), the primary component of the AP convertase, C3i-Bb. To evaluate this hypothesis, we examined the uptake kinetics and binding equilibria for C3i dimer interaction with human blood cells in the absence and presence of CR1- and CR2-blocking mAb. C3i displayed dual uptake kinetics to B lymphocytes, comprising of rapid binding to CR1 and slower binding to CR2. The forward rate constants (k(1)) for CR1 and CR2, operating independently, differed ca. 9-fold (k(1)=193+/-9.4 and 22.2+/-6.0 x 10(3) M(-1)s(-1), respectively). Equilibrium binding of C3i to B lymphocytes was also complex, varying in strength by ca. 13-fold over the C3i concentration range examined. The maximum association constant (K(a, max)=109+/-27.2 x 10(7) l/mole) was ca. 9- and 6-fold greater, respectively, than those for CR1 or CR2 acting alone (K(a)=13.2+/-5.3 and 18.5+/-3.5 x 10(7) l/mole). The high avidity of the CR1-CR2 complex for C3i is consistent with its rates of C3i uptake and release being determined by CR1 and CR2, respectively.     

Expression of complement receptor 2 (CR2) on HTLY-1-infected lymphocytes and transformed cell lines

The expression of complement receptor 2 (CR2) has been demonstrated in established HTLV-1-transformed cell lines and in 12 studied de novo infected peripheral blood lymphocytes cultures, using 2 HTLV-1 sources. The simultaneous detection of CR2 and HTLV-1 antigens in both co-cultivated and supernatant-infected peripheral blood lymphocytes suggest that the increased CR2 expression is in tandem with the increasing HTLV-1 antigen expression. CR2 up-regulation seen during polyclonal activation is presumably in response to a viral protein, although a cellular factor has not been ruled out. Increasing CR2 expression during early infection suggests its possible involvement in selection or development of subsequent transformation events. Variable levels of CR2 in immortalized cell lines argue against its obligate expression of function in the maintenance of the transformed state. The expression of CR2 in cellular activation of T cells may be stage restricted. This study also expands the cellular distribution for CR2.     

The structure,genetic polymorphisms,expression and biological functions of complement receptor type 1 (CR1/CD35)

The complement system is comprised of soluble and cell surface associated proteins that recognize exogenous, altered, or potentially harmful endogenous ligands. In recent years, the complement system—particularly component C3 and its receptors—have been demonstrated to be a key link between innate and adaptive immunity. Complement receptor type 1 (CR1), the receptor for C3b/C4bcomplement peptides, has emerged as a molecule of immense interest in gaining insight to the susceptibility, pathophysiology, diagnosis, prognosis and therapy of such diseases. In this review, we wish to briefly bring forth the structure, genetic polymorphisms, expression and biological functions of CR1.     

CD4-independent binding of HIV-1 to the B lymphocyte receptor CR2 (CD21) in the presence of complement and antibody.

Complement and antibody contribute to infection-enhancement and possible expanded cellular tropism of HIV-1 in vitro through a process requiring complement receptors. Until now, however, the ability of HIV-1 to bind complement receptors has not been documented or characterized. We investigated whether antibody and complement permitted HIV-1 to bind to the B lymphocyte receptor, CR2 (CD21), in an effort to learn more about infection-enhancement, and also because CR2 can mediate B cell proliferation and antigen localization in lymphoid organs in other systems. HIV-1 incubated with antibody and fresh human serum as a source of complement bound approximately 10-fold greater to cells expressing CR2 than to HIV-1-permissive cells lacking this receptor. A similar effect was observed using cells which expressed CR2 but no CD4. This binding was minimal in heat-inactivated and C3-deficient sera, and was significantly reduced by the anti-CR2 MoAb, OKB7, but not by the anti-CD4 MoAb, OKT4a. Thus, complement and antibody acted in concert to facilitate the binding of HIV-1 to CR2 independently of CD4. CD4-independent binding of HIV-1 to CR2 was not sufficient to produce infection in Raji-3 cells. Titres of antibodies mediating CR2 binding correlated with antibody titres as measured by immunofluorescence (P < 0.01) and infection-enhancement (P < 0.05) but were discordant with titres of neutralizing antibodies, a result consistent with the utilization of CR2 for enhanced infection of cells. The ability of complement and antibody to facilitate the binding of HIV-1 to CR2 in the absence of CD4 provides new insights into mechanisms of HIV-1-induced immunopathogenesis and infection-enhancement.     

Macrophages in normal human bone marrow and in chronic myeloproliferative disorders: An immunohistochemical and morphometric study by a new monoclonal antibody (PG-M1) on trephine biopsies

Summary An immunohistochemical and morphometric study was performed on routinely processed trephine biopsies of the bone marrow in 30 normal individuals and in 90 patients with various subtypes of chronic myeloproliferative disorder. Using a new monoclonal antibody (PG-M₁) directed against a formalin-resistant epitope on macrophages and by employment of the Prussian blue reaction, quantitation of this cell population was feasible. Morphometric analysis revealed that the number of iron-laden macrophages represented only a fraction of the total number of histiocytic reticular cells. As could be expected, in polycythaemia rubra vera, no haemosiderin deposits were detectable, but the content of macrophages slightly exceeded that of the normal bone marrow. In chronic myeloid leukaemia 9 of 30 patients showed a significant increase in PG-M₁-positive reticular cell elements. These were consistent with pseudo-Gaucher cells, sea-blue histiocytes and intermediate cell types. Primary (idiopathic) myelofibrosis-osteomyelosclerosis was characterized by a significant increase in macrophages (25 of 30 patients). Involvement of macrophages in the complex mechanisms generating bone marrow fibrosis and angiogenesis and in bone remodelling (osteosclerosis) may be responsible for this finding.     

Generation and characterization of new monoclonal antibodies against swine origin 2009 influenza A (H1N1) virus and evaluation of their prophylactic and therapeutic efficacy in a mouse model

In 2009, a swine-origin influenza A virus – A(H1N1)pdm09 – emerged and has became a pandemic strain circulating worldwide. The hemagglutinin (HA) of influenza virus is a potential target for the development of anti-viral therapeutic agents. Here, we generated mAbs by immunization of baculovirus-insect expressing trimeric recombinant HA of the A(H1N1)pdm09 strain. Results indicated that the mAbs recognized two novel neutralizing and protective epitopes-“STAS” and “FRSK” which located near Cb and Ca1 antigenic regions respectively and were conserved in almost 2009–2016 influenza H1N1 stains. The mAb 12E11 demonstrated higher protective efficacy than mAb 8B10 in mice challenge assay. Both mAb pretreatments significantly reduced virus titers and pro-inflammatory cytokines in mice lung postinfection (p < 0.01), and showed prophylactic and therapeutic efficacies even 48 h postinfection (p < 0.05). Combination therapy using the mAbs with oseltamivir pre- and post-treatment showed synergistic therapeutic effect in mice model (p < 0.01). Further investigation for clinical application in humans is warranted.     

Immunocytochemical study of NR1, NR2A and NR2B subunits of NMDA receptor in frog retina (Rana ridibunda)

The NMDA receptors are ionotropic glutamate receptors that are involved in a variety of functions in the nervous system and in particular in the retina. They are composed of NR1 and NR2 subunits. The NMDA receptors have been fairly well studied in the retina of mammals, however, there is only limited information concerning these receptors in the retinas of lower vertebrates. The aim of the present study was to investigate immunocytochemically the NR1, NR2A and NR2B subunits of the NMDA receptors in the frog retina. Six primary antibodies were used. Three of them were directed to different splice variants of the NR1 subunit and the remaining three variants directed to NR2 subunits. All antibodies showed well expressed labeling in the frog retina. The labels had a punctate character and were located mainly in the inner and the outer plexiform layers. The results obtained indicate that the NR1, NR2A and NR2B subunits of NMDA receptor may participate in the glutamatergic neurotransmission from photoreceptors to second order retinal neurons, as well as from bipolar cells to third order retinal neurons. It has been proposed that in the frog retina, several subtypes of NMDA receptors exist each involved with different functions.