Binding of a specific subclass of immunoglobulins by a human seminal plasma component

Three-dimensional structures of avian beta-microseminoproteins: insight from the chicken egg-specific beta-microseminoprotein 3 paralog

Beta‐microseminoproteins (MSMBs) are small disulfide‐rich proteins that are conserved among vertebrates. These proteins exhibit diverse biological activities and were mainly reported to play a role in male fertility, immunity, and embryogenesis. In this work, we focused on the chicken MSMB3 protein that was previously depicted as an egg antibacterial protein. We report that MSMB3 protein is exclusively expressed in the reproductive tissues of laying hens (in contrast to chicken MSMB1 and MSMB2 paralogs), to be incorporated in the egg white during the process of egg formation. We also showed that chicken MSMB3 possesses highly conserved orthologs in bird species, including Neognathae and Palaeognathae. Chicken MSMB3 was purified from egg white using heparin affinity chromatography and was analyzed by top‐down and bottom‐up proteomics. Several proteoforms could be characterized, and a homodimer was further evidenced by NMR spectroscopy. The X‐ray structure of chicken MSMB3 was solved for the first time, revealing that this protein adopts a novel dimeric arrangement. The highly cationic MSMB3 protein exhibits a distinct electrostatic distribution compared with chicken MSMB1 and MSMB2 structural models, and with published mammalian MSMB structures. The specific incorporation of MSMB3 paralog in the egg, and its phylogenetic conservation in birds together with its peculiar homodimer arrangement and physicochemical properties, suggests that the MSMB3 protein has evolved to play a critical role during the embryonic development of avian species. These new data are likely to stimulate research to elucidate the structure/function relationships of MSMB paralogs and orthologs in the animal kingdom.

A Bayesian view of murine seminal cytokine networks

It has long been established that active agents in seminal fluid are key to initiating and coordinating mating-induced immunomodulation. This is in part governed by the actions of a network of cytokine interactions which, to date, remain largely undefined, and whose interspecific evolutionary conservation is unknown. This study applied Bayesian methods to illustrate the interrelationships between seminal profiles of interleukin (IL)-1alpha, IL-1beta, IL-2, IL-4, IL-5, IL-6, IL-9, IL-10, IL-12 (p70), IL-13, IL-17, eotaxin, granulocyte-colony stimulating factor (G-CSF), granulocyte macrophage-colony stimulating factor (GM-CSF), interferon (IFN)-gamma, keratinocyte-derived chemokine (KC), monocyte chemoattractant protein (MCP-1), macrophage inflammatory protein (MIP-1) alpha, MIP-1beta, regulated on activation normal T cell expressed and secreted (RANTES), tumour necrosis factor (TNF)-alpha, leptin, inducible protein (IP)-10 and vascular endothelial growth factor (VEGF) in a rat model. IL-2, IL-9, IL-12 (p70), IL-13, IL-18, eotaxin, IFN-gamma, IP-10, KC, leptin, MCP-1, MIP-1alpha and TNF-alpha were significantly higher in serum, whilst IL-1beta, IL-5, IL-6, IL-10, IL-17, G-CSF and GM-CSF were significantly higher in seminal fluid. When compared to mouse profiles, only G-CSF was present at significantly higher levels in the seminal fluid in both species. Bayesian modelling highlighted key shared features across mouse and rat networks, namely TNF-alpha as the terminal node in both serum and seminal plasma, and MCP-1 as a central coordinator of seminal cytokine networks through the intermediary of KC and RANTES. These findings reveal a marked interspecific conservation of seminal cytokine networks.

Heterosexual spread of HIV infection

Sexual transmission is the most common route of spread of human immunodeficiency virus (HIV), with heterosexual transmission of HIV infection accounting for 90% of those infected in 1992 and over 75% of the 10–12 million of those infected to date worldwide. Yet, heterosexual transmission is poorly understood. Since HIV can be transmitted from HIV-infected people who are asymptomatic as well as from those who have the acquired immunodeficiency syndrome (AIDS), we must better define the potential for transmission of HIV from HIV-infected individuals as well as the factors which influence the susceptibility of HIV-uninfected individuals.

Multiplex determination of murine seminal fluid cytokine profiles

Seminal fluid is known to be responsible for orchestrating mating-induced immunomodulation. Central to this process are numerous cytokines that modulate uterine leukocyte recruitment and trafficking. Despite this, a comprehensive analysis of the cytokine profile of murine seminal fluid is lacking. This study addressed this issue by using multiplex immunoassays to characterise the profile of interleukin (IL)-1α , IL-1β , IL-2, IL-3, IL-4, IL-5, IL-6, IL-9, IL-10, IL-12 (p40), IL-12 (p70), IL-13, IL-17, eotaxin, granulocyte-colony stimulating factor (G-CSF), granulocyte macrophage-colony stimulating factor (GM-CSF), interferon (IFN)-γ, keratinocyte-derived chemokine (KC), monocyte chemoattractant protein (MCP)-1, macrophage inflammatory protein (MIP)-1α , MIP-1β , regulated upon activation normal T-cell expressed and secreted (RANTES), and tumour necrosis factor (TNF)-α in fluid drawn from the seminal vesicles of single mice (n= 18). Their levels and ratios were compared with those found in serum. IL-1α , IL-1β , IL-2, IL-5, IL-9, IL-12 (p40), IL-12 (p70), IL-13, IL-17, GM-CSF, IFN-γ, MCP-1 and TNF-α levels were significantly higher in serum; IL-4, G-CSF, eotaxin, KC and RANTES exhibited the opposite trend. Based on these findings, we propose a model of mating-induced immunomodulation that implicates seminal eotaxin, RANTES and MIP-1α in the relocation and concentration of extravasated migrating endometrial eosinophils to the luminal epithelium. Furthermore, KC may participate in uterine neutrophil chemotaxis and activation. Eotaxin and MIP-α , together with IL-1β and IL-9, may also enhance further cytokine synthesis for endometrial antigen-presenting cell recruitment for processing paternal ejaculate antigens. IL-4 and G-CSF could also minimise deleterious cell-mediated immunity and modulate IFN-γ production, thereby supporting the establishment of pregnancy.

Human seminal plasma antibody-binding proteins

PROBLEM

The physiological role of antibody-binding proteins in human seminal plasma and the potential role of these proteins in infertility is relatively unknown.

METHOD OF STUDY

Literature on antibody-binding proteins.

RESULTS

Human seminal plasma has a diverse effect on immune function of the reproductive tracts. This review describes (1) the presence of receptors like proteins that can react with monoclonal antibodies against Fcgamma receptors III (Fcgamma RIII) but are distinctly different from Fcgamma RIII; (2) IgG binding factors (IgGBF), a group of low molecular weight proteins that are capable of binding human IgG; (3) other proteins that can bind antibodies, such as prolactin-inducible protein and three other novel proteins that we have discovered. These proteins potentially all have the ability to reduce the interactions between antisperm antibodies and effector components of the immune system, such as phagocytic cells.

CONCLUSIONS

Human seminal plasma contains proteins that can bind antibodies. However, to date our knowledge of these proteins especially, whether they have a physiological role in either the male and female reproductive tracts is limited.

Inhibitory effects of human seminal plasma on an ELISA used to detect anti-sperm antibodies: implications for the determination of sperm quality

The in vitro inhibitory effect of human seminal plasma on an ELISA used to detect anti-sperm antibodies have been observed. The mean inhibition rate of seminal plasma samples from 75 men was 61.5+/-23.1%. The inhibition rate of 29 samples from normal sperm group was 71. 14+/-18.25%, while that of 46 samples from the abnormal sperm group was 55.43+/-23.98%. The results show that human seminal plasma from semen with high quality sperms possesses a high inhibitory rate to anti-sperm antibody reactions, suggesting its efficiency for immunosuppression of humoral immune reactions. Its possible implications are discussed.

beta-Microseminoprotein/prostatic secretory protein is a member of immunoglobulin binding factor family

Human seminal plasma contains a factor that binds human IgG, designated as immunoglobulin binding factor (IgBF). Under reducing condition IgBF interacts with anti-Leu-11b, a murine monoclonal antibody raised against human FcgammaRIII/CD16. IgBF shows no binding activity under non-reducing condition. Three components having IgBF activity were separated by HPLC and their amino acid sequences determined. The main IgBF showed structural identity to beta-microseminoprotein (beta-MSP), prostatic secretory protein of 94 amino acids (PSP94) and beta-inhibin. The slight variation in the reported sequences of these proteins has been attributed to analytical error. In the present study the molecular masses of main IgBF and beta-MSP/PSP94 were found to be identical by mass spectrometry. In addition, a large component of IgBF and a shorter beta-MSP consisting of 93 amino acids were identified. The binding of beta-MSP for human IgG and anti-Leu-11b antibody is demonstrable only under reducing condition, determined by Western blot analysis. The present data clearly show that IgBF is a family composed of at least three isoforms. One of the members is beta-MSP/PSP94. This family should be designated as IgBF.

Anti-seminal plasma antibodies associated with infertility: II. Comparative investigation of human antibody binding to normo-, astheno-, and azoospermic seminal plasma antigens

PROBLEM

Sera from infertile patients with elevated reactivity against normozoospermic seminal plasma (NSP) have been selected to investigate human antibody binding to seminal fluid antigens present in abnormal ejaculates.

METHOD

Sera from 32 idiopathically infertile patients and 44 control sera from fertile individuals were examined by ELISA against: 1) pooled seminal plasma from asthenozoospermic ejaculates (AsthSP), 2) pooled seminal plasma from patients with aspermatogenic azoospermia (AzooSP), and 3) chromatographic fractions from NSP, AsthSP and AzooSP.

RESULTS

Of 32 patients positive for anti-NSP antibodies, only four exhibited increased reactivity to whole AsthSP and/or AzooSP, while 14 recognized antigens of different Mr and various distributions in the corresponding chromatographic fractions.

CONCLUSION

Targets of human anti-NSP antibodies might be lacking, less concentrated, and/or modified in AsthSP and AzooSP. These findings suggest their physiological importance and the possible relevance of the observed auto- and iso-immune responses to infertility.

A putative mechanism for the non-specific uptake of intact radiolabelled monoclonal antibodies in the testes and prostate

Non-specific testicular accumulation of radiolabelled intact anti-CEA monoclonal antibody (MAb), (A431/26, Behringwerke AG) was observed in 11 out of 12 patients with the testes and prostate included in the examination field at radioimmunoscintigraphy (RIS). Previous studies have shown that placental alkaline phosphatase (PLAP) serves as an Fc-receptor, mediating IgG transport through the placenta. A closely related protein, the germ cell alkaline phosphatase (GCAP), is expressed in the testes. The testicular uptake of IgG is observed only when intact but not fragmented MAbs are used, indicating involvement of Fc-receptors. MDCK cells (dog kidney cell line) transfected with the plasmid pSVT7 containing the GCAP gene were shown to acquire the capacity to both express membrane bound GCAP and to bind IgG on the cell surface. This might indicate that GCAP is responsible for the non-specific accumulation of intact MAb in the testes and prostate often observed when intact murine MAbs are used for radioimmunolocalization (RIL).

Identification of human seminal plasma components that bind IgG2 variant

Human seminal plasma (hsp) contains soluble proteins capable of binding immunoglobulin (Ig) G. Two novel components with estimated molecular sizes of 90 and 21 kD interact specifically with a variant of IgG2 found in 20% of human sera tested. The common IgG2 present in human sera and other subclasses of IgG did not bind with the hsp components. The present findings shows that the interacting IgG2 is a variant and not the common or prevalent species. The 90-kD component of hsp with IgG2 binding property is probably a nonglycosylated protein, whereas the 21-kD component is a glycosylated protein. The 90- and 21-kD components were detected in 20% of hsp specimens tested. Thus they are not present in the majority of hsp. Since the IgG2 binding components of hsp and the serum IgG2 variant are found in 20% of men and 20% of individuals, respectively, they can be used as genetic markers.

IgG4 binding factor in human seminal plasma identified as heavy chain of immunoglobulin

Human seminal plasma contains a factor that binds human immunoglobulin G (IgG). The factor has an estimated M(r) of 50 kD and interacts specifically with human IgG4. It does not bind other subclasses of human IgG or IgGs of other mammalian species tested. The factor was purified by affinity chromatography on protein G column. The 50-kD component was eluted in the adsorbed fraction and immunostained with monoclonal antibodies against heavy chain (gamma) of IgG. Purified subclasses of human serum IgG were separated into heavy and light chains by sodium dodecyl sulfate polyacrylamide gel electrophoresis under reduced condition. The heavy chains of all subclasses of IgG bound IgG4. The present findings suggest that the 50-kD IgG4 binding factor of human seminal plasma is the heavy chain of IgG.