The complement system in human reproduction

Regulation of the complement system in reproduction is unique inasmuch as reproductive tissues represent the only condition where allogeneic interactions occur naturally. Both allogeneic extraembryonic membranes and semen that contact and interact with maternal cells and tissues must avert complement-mediated damage to ensure reproductive success. Several regulators of complement activation exist. Membrane cofactor protein (MCP) and decay accelerating factor (DAF) inactivate C3 and C5 convertases on cell surfaces. In addition, CD59 inhibits the membrane attack complex (MAC) of the complement cascade. Strong expression of these membrane glycoproteins by trophoblast and amniotic epithelium has been observed. MCP, DAF, and CD59 likely safeguard extraembryonic tissues from complement damage originating from maternal and fetal blood or amniotic fluid. Different reproductive tract fluids vary in complement levels. With the exception of ovarian follicular fluid, these levels are generally much less than those in blood. Endometrial and cervical content of C3 appear to be regulated by hormones. These observations suggest that the effects of complement activation may vary in reproductive tissues. MCP is absent from the surfaces of oocytes. Sperm express MCP and DAF in discrete areas that would not be associated with the known complement-regulatory functions of these proteins. Seminal plasma contains MCP and the MAC inhibitor SP-40,40 but not DAF.SP-40,40 may exemplify how complement-regulatory proteins perform alternative functions as it interacts with molecules other than complement components. We have reviewed aspects of the complement system that relate to allogeneic interactions in reproduction and that suggest fruitful areas for further research.

Inhibition of immunoglobulin (Ig)G-Fc-mediated cytotoxicity by seminal plasma IgG-Fc receptor III antigens

OBJECTIVE

To determine if the presence of soluble immunoglobulin (Ig)G-Fc receptor III (Fc gamma RIII) antigens in human seminal plasma interfere with IgG-Fc-mediated effector functions.

DESIGN

An antibody-dependent cellular cytotoxicity (ADCC) assay was used as a model for IgG-Fc-mediated effector functions. Human red blood cells (RBC), labeled with 51Cr were sensitized with rabbit anti-RBC and used as targets for peripheral blood leukocyte (PBL) effector cells. Cytotoxicity was measured by assessing the release of 51Cr from RBC.

INTERVENTIONS

(1) Seminal plasma was added at different concentrations to the ADCC, and inhibitory effects were measured. (2) The level of seminal plasma interaction in ADCC was studied by comparing ADCC results in the presence and absence of seminal plasma with findings of target and effector cells that had been preincubated with seminal plasma. (3) The role of seminal plasma Fc gamma RIII in inhibiting ADCC was studied by coincubating seminal plasma with monoclonal antibodies (MAs) Leu 11b that block Fc gamma RIII binding sites. Two isotype-matched MA controls were used at identical concentrations.

RESULTS

(1) Seminal plasma dose dependently inhibits ADCC. (2) Seminal plasma inhibition of ADCC occurs at the level of IgG-Fc interaction with effector cell Fc gamma receptors. (3) Inhibitory effects of seminal plasma on ADCC can be specifically blocked by coincubating seminal plasma with MAs Leu 11b that block Fc gamma RIII binding sites.

CONCLUSIONS

Seminal plasma Fc gamma RIII antigens interfere with IgG-Fc-mediated effector functions. This mechanism could play a beneficial role in controlling potentially harmful antipaternal immune responses.

A vitronectin-receptor-related molecule in human placental brush border membranes

The heterodimeric vitronectin receptor (VNR) and platelet glycoprotein IIb/IIIa (GPIIb/IIIa) are two members of the integrin family of cell adhesion receptors that share the same beta subunit (GPIIIa). These proteins are involved in binding to vitronectin, fibrinogen and fibronectin and in cytoskeleton-membrane interactions. The present study shows that the human placental syncytiotrophoblast brush border membrane contains a heterodimer of subunit Mr values of 140,000 and 90,000 (non-reduced) or 125,000 and 100,000 (reduced). This protein was recognized by a monoclonal antibody to GPIIIa, rabbit antisera to the VNR and a human alloantiserum to GPIIIa. Brush border VNR-related protein bound to an immobilized peptide containing the Arg-Gly-Asp sequence and, less avidly, to immobilized fibrinogen. Only a small fraction of brush border VNR was associated with a cytoskeleton fraction. Membrane-bound brush border GPIIIa was distinct from that of platelets in its resistance to digestion by trypsin and Staphylococcus aureus V8 protease, and had a slightly lower mobility on SDS/PAGE. In addition, lectin-binding studies indicate glycosylation differences between microvillar and platelet GPIIIa heterodimers. Thus, although placental syncytiotrophoblast expresses a beta 3 integrin in its apical brush border, differences in protease sensitivity and carbohydrate content suggest that it may lack or mask certain antigenic determinants. This may be beneficial in avoiding harmful maternal alloantibody responses during pregnancy. Immunohistology showed that the VNR was present in syncytiotrophoblast apical but not basal plasma membranes, and was absent from other forms of trophoblast. The brush border VNR could function in localizing Arg-Gly-Asp-sequence-containing plasma proteins to the materno-trophoblastic interface.

Serological markers of sexually transmitted diseases associated with HIV-1 infection in pregnant black women

While the prevalence of HIV-1 is increased in women attending sexually transmitted diseases (STD) clinics, in South Africa little is known about STD risk factors in women infected with HIV-1 in the general population. Serological markers of STDs were investigated in a cohort of 21 pregnant women, who were found to be carriers of HIV-1, and in 42 age- and residentially matched uninfected pregnant women. The rapid plasma reagin test (RPR) was positive in 33% of the HIV-1- infected women (P less than 0.05 compared with controls). The specific treponemal fluorescent antibody absorbed test (FTA-abs) was positive in 43% of the HIV-1-infected women (P less than 0.05 compared with controls). Similarly the prevalence of chlamydial IgG antibodies as measured by enzyme-linked immunosorbent assay was 95% (P = 0.026 compared with controls). Markers of hepatitis B infection were similar to both groups. Pregnant women with HIV-1 infection in the Johannesburg area have an increased seroprevalence of markers of STDs and more data are required on the attitudes and sexual activity of these women in order to target AIDS and education information.

Syncytiotrophoblast brush border proteins recognized by monoclonal antibody TRA-2-10 and rabbit anti-TLX sera

Different subsets of placental trophoblast epithelium are directly exposed to the maternal immune system during pregnancy and consequently represent major elements in allogeneic interactions. It has been proposed that the trophoblast--lymphocyte cross-reactive (TLX) alloantigen system is involved in maternal allogeneic recognition during pregnancy. Monoclonal antibody TRA-2-10 putatively recognizes TLX antigens, but its reactivity with trophoblast and normal tissues has not been documented in detail. In this report, immunohistological investigations revealed that TRA-2-10 recognizes all subsets of trophoblast in addition to amniotic and seminal vesicle epithelia. Immunoblotting demonstrated reactivity with glycoproteins of 55,000 and 65,000 mol. mass under non-reducing conditions on various cell types. These proteins displayed tissue-specific size variations and individuals varied in the amounts expressed of the two species. On the basis of blocking and immunoprecipitation experiments, TRA-2-10 reactive antigens are recognized by rabbit anti-TLX sera and are potential TLX antigen candidates. However, TLX antigens are found in seminal plasma whilst TRA-2-10 reactive antigens are not. Both TLX and TRA-2-10 antigens appear related if not identical to membrane cofactor protein (MCP) by virtue of shared molecular characteristics and blocking of lymphocyte binding of monoclonals to MCP by polyclonal anti-TLX. Extra-embryonic membranes are thus richly endowed with a complement regulatory protein which could facilitate their roles in protection of the fetus by avoidance of harmful maternal immune response amplification.

A role for TLX antigens in pregnancy

Maternal responses to allotypic TLX antigens are proposed as necessary in the immunological maintenance of human pregnancy. The TLX antigens are strategically and strongly expressed in semen and on the extraembryonic tissues which form the anatomical materno-fetal interfaces. Recent findings suggest that CD 46 proteins (a membrane cofactor which protects self tissues from autologous complement damage) in association with the activated complement component, C 3b produce a novel antigenic epitope recognized by both rabbit and human anti-TLX antisera. Control of TLX immunity involves an idiotype-antiidiotype network. We now report the development of rabbit antiidiotypes specific for cross-reactive idiotypes on human anti-TLX IgG antibodies. These antiidiotypes appear to recognize different TLX allotypes and will be useful for gaining additional insight into the immunogenetics of human reproduction.

Major histocompatibility antigens in transplanted human hearts before perfusion

The expression of major histocompatibility class I and II antigens is described in human normal donor hearts before perfusion with recipients' blood. Class I and II major histocompatibility antigens were found on interstitial but not on myocardial cells. Endothelial cells accounted for most of the generic class I reactions (that is, W6/32 and beta 2 microglobulin), and endothelial cells accounted for most of the HLA-DR and -DP reactivity. HLA-DQ antigens were not found in this series of normal donor hearts. The earliest time we were able to identify HLA-DQ antigens during the follow-up biopsies from these patients was 1 week after the allograft had been in place. Macrophages accounted for little of the class II reactivity. Variations in the HLA-DQ antigen expression on endothelial cells may be useful in the follow-up of transplanted hearts, considering that these antigens have been found to be more susceptible to the effects of interferon-gamma than either HLA-DR or -DP.

Trophoblast immunity in human pregnancy defined by antiidiotype

Successful reproduction in mammals requires the mother to immunologically accept genetically disparate tissues. Allotypic trophoblast antigens (TLX) are thought to be responsible for influencing maternal acceptance of the feto-placental graft, and faulty regulation of immunity to TLX antigens has been associated with recurrent pregnancy losses. In this report, rabbit antiidiotype (RAb2) was produced to a human TLX antibody (Ab1). This RAb2 detected TLX cross-reactive idiotypes (CRI) on antitrophoblast IgG from women with normal and abnormal pregnancies. These findings support an hypothesis that women respond immunologically to allotypic trophoblast antigens, and that idiotype-antiidiotype regulation of this response is characteristic of normal pregnancy.

Occurrence of other reproductive failures among women with recurrent spontaneous abortion

We have previously reported an association between recurrent spontaneous abortion and ectopic pregnancy. We now report that not only ectopic pregnancy, but also other reproductive failures including hydatidiform moles, preterm births, and stillbirths are also associated with recurrent spontaneous abortion. The obstetrical histories of 455 women who had experienced two or more consecutive spontaneous abortions were studied for the occurrence of term births, preterm births, stillbirths, spontaneous abortions, ectopic pregnancies, and hydatidiform moles. The observed frequencies of these reproductive outcomes were compared with the expected frequencies of 920 term births, 80 preterm births, five stillbirths, 150 spontaneous abortions, 14.5 ectopic pregnancies and 0.5 molar pregnancies per 1,000 livebirths. The 455 women had experienced 1,968 pregnancies of which 184 were term births, 30 were preterm births, 16 were stillbirths, 1,669 were spontaneous abortions, 63 were ectopic pregnancies, and six were molar pregnancies. The ratio of observed to expected values was term births 0.1, preterm births 1.6, stillbirths 14.0, spontaneous abortion 6.6, ectopic pregnancy 2.6, and molar pregnancy 7.1. The gravid specific proportions of reproductive outcomes were constant suggesting comorbidity or common cause(s). The commonality that links these types of reproductive failure will provide insight into the mechanisms of reproductive wastage.

Immunogenetic studies of soluble Fc receptor (CD16) antigens in human seminal plasma

Two forms of CD16 Fc receptors (FcRIII) have been defined on human leukocytes. Type 1, present on polymorphonuclear neutrophils (PMN), expresses the NA alloantigen system and type 2, present on natural-killer (NK) cells and macrophages, has no known polymorphic variations. We have described the presence of soluble FcRIII antigens in human seminal plasma (SP). These SP antigens retain an affinity for IgG-Fc and are biochemically distinct from leukocytic FcRIII. Their origin within the male reproductive tract and how they relate to FcRIII types 1 and 2 were not known. By using monoclonal antibodies CLB/Gran 11 and Leu 11c that differentially react with FcRIII type 1 and type 2 from different individuals, we studied how SP FcRIII antigens relate to leukocytic FcRIII. CLB/Gran 11 and Leu 11c reactivities with PMN and NK cells from a selected panel of male donors were compared with enzyme-linked immunosorbent assay reactivities of CLB/Gran 11 and Leu 11c with SP samples from these donors. The reactivity pattern with SP samples was shown to be different from findings with donors' PMN, but it corresponded with their NK cells. Our results indicate that SP FcRIII antigens do not manifest the polymorphic variations that are detected by CLB/Gran 11 and Leu 11c on PMN. These findings suggest that SP FcRIII antigens do not originate from PMN.

Antigens of immunoglobulin G-Fc receptor III in human male reproductive tract accessory glands

We have documented the presence of soluble antigens of immunoglobulin (Ig)G-Fc receptor type III (FcRIII) in human seminal plasma that retain an affinity for the Fc fragment of IgG. The origin of these FcRIII antigens within the male reproductive tract was not known. By using polyclonal and monoclonal antibodies directed against different epitopes on FcRIII molecules, we demonstrated FcRIII reactivity in human prostate and seminal vesicle epithelial cells as well as in their glandular secretions. The FcRIII monoclonal antibody reactivity was removed by absorption with either seminal plasma or polymorphonuclear leukocytes that express FcRIII. Absorption of FcRIII monoclonal antibody with polymorphonuclear leukocytes also removed the reactivity with seminal plasma and vice versa. These data show for the first time that male accessory glands are a source of soluble FcRIII antigens.

Conversion of IgG-mediated complement-dependent cytotoxicity by reducing reagents

Reducing reagents used in complement-dependent crossmatches reduce IgM but not IgG. A positive IgM crossmatch is not an absolute contraindication to allografting. We have studied an alloantiserum from a patient with 100% panel reactive antibody awaiting heart transplantation whose serum was reduced. Absorption of this serum with the patient's erythrocytes or leukocytes had no effect on the third-party cytotoxicity. Absorption with third-party plasma or serum was without effect. Crossmatch of this serum with an HLA-A,B,C-identical nonrelated target was positive, whereas crossmatches with the patient's HLA-identical siblings were negative. Crossmatches with the patient's five children showed one strong, three intermediate, and one weak cytotoxic reactions. No antibody-dependent cellular cytotoxicity activity was observed. Fluorescence-activated cell sorter analyses showed no IgM but strong IgG1 antibody present before and after reduction of the serum. Our data indicate some IgG antibodies are reducible. The transplantation outcome in the presence of reducible IgG alloantibodies is not known, but it is possible these antibodies are associated with graft failures in patients observed to have positive standard crossmatches that become negative in the presence of reducing reagents.

Lactoferrin binding molecules in human seminal plasma

During ejaculation, the iron binding protein lactoferrin binds to sperm and forms a major component of sperm-coating antigens. Physicochemical properties of lactoferrin in seminal plasma (SP) and on sperm differ from those of purified lactoferrin. These differences have been attributed to the binding of unknown seminal macromolecules to lactoferrin. We have studied lactoferrin binding molecules in SP. The SP samples were coated onto microtiter plates and tested for binding of biotinylated lactoferrin. SP was found to specifically bind biotinylated lactoferrin. This binding was competitively inhibited by coincubation with unlabeled lactoferrin but was not affected by control incubations done with human IgG or transferrin. Lactoferrin binding molecules in SP were biochemically characterized by using SDS-PAGE and ligand blotting. Biotinylated lactoferrin bound to SP molecules of approximately 120, 60 and 30 kDa. No binding was observed with biotinylated transferrin. The presence of molecules that associate with lactoferrin in SP was further studied by using crossed immunoelectrophoresis. Lactoferrin in SP immunoprecipitated as two peaks, one of which corresponded to purified lactoferrin. These results suggest that some lactoferrin molecules in SP are free and that others are associated with lactoferrin binding molecules. Binding of lactoferrin to lactoferrin binding molecules appears to change its physicochemical properties and thus could influence its biologic activity and its affinity to sperm.

Congenital aplasia of seminal vesicles: absence of trophoblast-lymphocyte cross-reactive antigens from seminal plasma

Our studies show that TLX antigens are absent from seminal plasma of a patient with bilateral aplasia of seminal vesicles. This is supportive for an origin of seminal plasma TLX antigens from seminal vesicles. The release of TLX antigens by seminal vesicles could represent a mechanism of priming mothers immunologically for normal implantation and pregnancy.

Preliminary clinical study of transferrin-adriamycin conjugate for drug delivery to acute leukemia patients

Seven patients with acute leukemia were treated intravenously with low doses of transferrin-Adriamycin conjugate. The total amount of drug given each patient was far below known toxicity levels for free Adriamycin. The number of tumor cells in peripheral blood diminished in treated patients, and bone marrow aspirates showed no evidence of disease progression. Two patients gave a febrile response and no hypersensitivity reactions were observed. Results of parallel basic research have shown that transferrin receptors on acute leukemia cells bind transferrin-Adriamycin conjugates, and kill by mechanisms at either the plasma membrane or nuclear levels, or both. Such conjugates may provide an alternative to monoclonal antibody drug targeting.

Heat treatment of serum and plasma induces false positive results in the antiphospholipid antibody ELISA

We found that levels of antiphospholipid antibodies (aPLA), measured with an ELISA increase if serum or plasma samples are heated. The phenomenon is dependent on duration and degree of heating, optimum levels being reached at 3 h at 56 degrees C. Negative samples become positive after heating. The heating effect is more pronounced for IgG-aPLA than for IgM-aPLA and is not observed for adsDNA, atetanus or lymphocytotoxic antibodies. The presence of serum/plasma components in addition to IgG is essential for the phenomenon to occur. Ultracentrifugation and mixing experiments with isolated IgG did not enable us to explain our observations. Nevertheless, knowledge of this phenomenon is of practical importance.

Immunohistologic evidence that villitis in human normal term placentas is an immunologic lesion

Villitis of unestablished origin is a lesion in placentas from normal and high-risk pregnancies. We have studied villitis areas in 25 normal term placentas for immune cells, coagulation components, and endothelial markers. Villitis areas were filled with activated (HLA-DR, HLA-DP, and HLA-DQ reactive) macrophages. B lymphocytes were not identified, and T lymphocytes were of the helper (CD4) phenotype. Antibodies to coagulation components revealed perivascular and trophoblastic basement membrane deposits of factor IX, increased numbers of platelets, and fetal stem vessels that did not react with endothelial markers. These findings suggest helper T lymphocytes activate macrophages that mediate coagulation activation and alter endothelium. This combination of immunologic events results in tissue changes that are histologically diagnosed as villitis. It is not known what triggers these immunologic events, but the finding of villitis in normal placentas suggests the causative factor(s) is present in all pregnancies.

Regulation of immunity to extraembryonic antigens in human pregnancy

Pregnancy results in the immunologic challenge of the female to a wide variety of allogeneic antigens. Particular attention has been given to antibodies directed to allotypic trophoblast antigens (TLX), for trophoblast form the true allograft interface between mother and fetus. Studies found that antibodies to paternal TLX allotypes are produced in women suffering from secondary recurrent abortions. These TLX antibodies are not directed to classical HLA private epitopes. In this report, treatment of lymphocytes with papain to remove HLA Class I did not decrease TLX antigen densities. These results suggest TLX antibodies are not directed to Class I epitopes, public or private. The allotypic nature of TLX antigens requires that a pregnant female must be able to regulate TLX immune responses to avoid rejection of the conceptus. One mechanism to specifically and systemically regulate TLX immunity is the idiotype anti-idiotype network. We provide preliminary evidence in this report for the presence of TLX idiotype network in a normal primigravida. Initially, no antipaternal TLX antibodies were detected in the serum of the primigravida, suggesting no TLX immunization had occurred. However, separation of Ab1 from Ab2 by absorption of primigravida serum with 2 degrees aborter Ab1 resulted in seroconversion. The primigravida's Ab1 was cytotoxic for paternal and 3rd-party lymphocytes in a non-HLA-restricted pattern. Primigravida's Ab2 was recovered from the Ab1 matrix by competitive elution by using platelets as source of TLX antigen. The Ab2 was found to inhibit cytotoxicity by 2 degrees aborter Ab1 as well as primigravida Ab1. This is evidence that the Ab2 recognizes a cross-reactive idiotype (CRI) on TLX antibodies.(ABSTRACT TRUNCATED AT 250 WORDS)

Occurrence of ectopic pregnancy among women with recurrent spontaneous abortion

Ectopic pregnancy is a major health problem accounting for about 10% of all maternal mortality. To determine whether patients with a history of recurrent spontaneous abortion (RSA) have a higher frequency of ectopic pregnancy than the general population, the obstetrical histories of 630 patients with a diagnosis of RSA from two centers were studied. Thirty-eight of 376 USA women, (10%) and 10 of 193 British women (5%) previously had suffered an ectopic pregnancy. These data provide an overall prevalence of 9% for ectopic pregnancy among patients who recurrently abort. The total number of pregnancies was 1,716 in the USA group and in the British group was 1,270, for a total of 2,986 including live births, stillbirths, abortions, hydatidiform moles, and ectopic pregnancies. In the US series, 45 of the 1,716 pregnancies were ectopic. If these women had the same relative proportion of ectopic pregnancies as the general population, there should have been 20.6 ectopic pregnancies. This represents a 2.2-fold increase in patients with a history of RSA. There was no association between pregnancy order and occurrence of ectopic pregnancy. The prevalence of known risk factors for ectopic pregnancy in patients with a history of ectopic pregnancy was PID, 3%; tubal surgery, 20%; and used IUD, 3%. Seventy-four percent of the women had no identifiable risk factor. These results suggest a comorbidity for ectopic pregnancy and RSA which may indicate shared etiologies.

Recent advances in cancer research: drug targeting without the use of monoclonal antibodies

Cancer research in drug targeting has focused on the use of monoclonal antibody conjugates of drugs. This paper discusses the use of ligand conjugates of drugs to deliver to receptors on cancer cells. We have used transferrin coupled to adriamycin, and report these conjugates specifically bind and kill cancer cells in culture. Our studies of the mechanism show targeted plasma membranes are compromised for NADH ferricyanide reduction, and targeted cells lose diferric transferrin reductase activity. These results indicate that the binding of transferrin-adriamycin conjugates to transferrin receptors on either isolated plasma membranes or viable tumor cells causes an inhibition of redox reactions that are essential for growth. Since transferrin receptors are endocytosable, ligand-drug conjugates also are delivered to the interior of targeted cells where other mechanisms of killing can be employed. This novel method of drug delivery circumvents the need for monoclonal antibodies, and more investigation of the system may allow a controlled clinical study of its effectiveness.

Villitis in normal term human placentae: frequency of the lesion determined by monoclonal antibody to HLA-DR antigen

Chronic villitis is a placental lesion of unestablished etiology. It is characterized by destruction of chorionic villi with a mononuclear infiltrate and focal areas of fibrinoid necrosis. The lesion frequently is seen in normal placentae, yet more lesions have been reported in placentae from abnormal pregnancies. We measured the extent of villitis in 25 normal term placentae by using both light microscopy and immunocytology for class II (HLA-DR) antigens of the major histocompatibility complex. HLA-DR antigens were found to be characteristic of villitis areas. Normal placentae showed striking variations in the incidence of villitis, but these variations did not correlate with clinical outcome.

Recurrent spontaneous abortion

The laboratory diagnosis and clinical management of unexplained recurrent spontaneous abortion (RSA) patients is a controversial issue in contemporary obstetrics. In this report, the results of laboratory investigations and immunotherapy of RSA patients referred to our Center since 1986 are detailed. Our analyses have resulted in grouping RSA patients into primary (1 degree), secondary (2 degrees), and unexplained classifications. Laboratory evaluation criteria included assays for both complement-dependent and complement-independent antipaternal antibodies as well as histocompatibility antigen tissue typing for HLA, A, B, C, and DR antigens. In addition, mixed lymphocyte cultures (MLC) were performed to assess the degree of HLA-D locus compatibility between couples and to test for the presence of MLC inhibitors in maternal blood. Immunotherapy options and the rationale for their use are given and preliminary outcome data are presented from randomized double-blinded, placebo-controlled clinical trials.