Molecular dissection of human testicular germ cell differentiation with monoclonal antibodies

Characterization of a 50-kDa component of epithelial basement membranes using GDA-J/F3 monoclonal antibody

Using the monoclonal antibody GDA-J/F3, a 50-kDa noncollagenous component of human skin basement membrane zone was identified. Immunofluorescence stainings of normal human skin with the GDA-J/F3 antibody showed a linear fluorescence decorating the basement membrane zone. With immunoelectron microscopy, the epitope was localized to the insertion points of the anchoring fibrils into the lamina densa. The antigen is distinct from collagen VII, from the main structural protein of the anchoring fibrils, and from several other structural molecules of the basement membrane zone, because the GDA-J/F3 antibody did not react with purified basement membrane components in vitro. In serum-free cultures, the antigen was synthesized and secreted by normal and transformed human keratinocytes and to a lesser extent by normal human skin fibroblasts. Immunoprecipitation of radiolabeled epithelial cell-conditioned medium with the GDA-J/F3 antibody yielded two polypeptides that migrated on SDS-polyacrylamide gel electrophoresis with apparent molecular masses of 46 and 50 kDa under nonreducing conditions. Using reducing gels, only the 50-kDa polypeptide was observed. The antigen was resistant to digestion with bacterial collagenase but sensitive to trypsin and pepsin. It also bound to heparin and DEAE cellulose at low ionic strength and alkaline pH. These findings indicate that the GDA-J/F3 antigen is a small globular disulphide-bonded protein with a potential to interact with basement membrane proteoglycans. Integration of the GDA-J/F3 antigen into the histoarchitecture of the dermo-epidermal junction is dependent on the presence of collagen VII, because the GDA-J/F3 epitope was missing in several patients with a genetic blistering disorder of the skin, epidermolysis bullosa dystrophica, who lacked collagen VII and anchoring fibrils.

Lack of expression of HLA antigens on immature germ cells from ejaculates with antisperm antibodies

PROBLEM

The lack of expression of HLA antigen on immature germ cells from ejaculates with antisperm antibodies has been reported.

METHOD

The expression of human leukocyte antigens on immature germ cells from ejaculates with antisperm antibodies (ASA) was investigated by indirect immunofluorescence using a panel of monoclonal antibodies (MAb) and automated flow cytometry. Patients were divided into two groups: fertile (prevasectomic; N = 10), and ejaculates with ASA (10 samples with IgG and IgA ASA, and five semen samples with only IgG ASA). ASA were detected on sperm using the direct immunobead test. After centrifuging semen samples on a Ficoll-Hypaque gradient, round cells obtained at the gradient interface were gated by a flow cytometer. The "immature germ cell window" was defined in terms of cellular volume and granularity.

RESULTS

The percentage of gated round cells from semen samples that reacted with anti-CD45 was always less than 5%, and with anti-CD44 less than 3%. This lack of reactivity of gated round cells with MAb specific for leukocytes and epithelial cells suggests that they were immature germ cells. Immature germ cells were unreactive with W6/32 and anti-beta-2-microglobulin MAb, which suggests that these cells do not express HLA class I molecules. Similarly, no reactivity of the immature germ cells with the MAb that recognize HLA class II molecules was found. No significant differences were observed in the expression of HLA molecules on immature germ cells between the different semen samples studied: fertile, and ejaculates with ASA.

CONCLUSION

The presence of ASA in ejaculate is not associated with abnormal HLA antigen expression on immature germ cells.

Impaired antibody diffusion within the cytoplasmic membrane-fibrous sheath interspace of the human sperm tail

Monoclonal and polyclonal antibodies specific for the fibrous sheath (FS) were used to assess their diffusion within the subcytoplasmic membrane space of the human sperm tail. Using indirect immunofluorescence (IIF) and immunogold electron microscopy (IEM), the staining of the entire FS with these antibodies was observed only when the spermatozoa were completely demembranated by detergents or dried onto slides. Partial damage to sperm cytoplasmic membranes by freezing and thawing resulted in segmental staining of the FS. The IEM of such spermatozoa with the antibodies revealed the distribution of gold particles on the FS in denuded areas only and adjacent segments which retained their cytoplasmic membrane were not stained. These results indicate that partial disruption of the sperm plasma membranes does not lead to free diffusion of antibodies within the cytoplasmic membrane-FS interspace. This property appears to be unique to sperm cells and is due to their specialized structural organization.

Antigenic determinants of human sperm tail fibrous sheath proteins

Mouse anti-fibrous sheath antisera (MAFA) produced by immunizing mice with purified preparations of human sperm tail fibrous sheath (FS) reacted with the principal piece of less than 10% of freshly isolated spermatozoa which were immotile and probably dead. Following their demembranation by detergents or repeated freezing and thawing, all spermatozoa were stained. This was also demonstrated on spermatozoa dried onto slides, but the undiluted xenoantisera showed additional reactivity with the acrosomal zone (AZ). Using immunogold electron microscopy, the target antigens were ultrastructurally localized to the FS, and a few spermatozoa showed some reaction at the AZ subacrosomal perinuclear theca. Following titration of the antibodies, the anti-AZ-reaction became undetectable at a dilution of 1:20 while their reactivity with the principal piece continued to a 1:400-dilution. These results indicated that the xenoantisera probably contained an additional unrelated antibody component which reacted with the AZ. Western blotting and staining of purified FS with MAFA detected seven major protein bands with MW ranging between 25 kDa and 97.4 kDa. In human testes, the 1:50 diluted MAFA reacted with sperm tails only, indicating the late expression of the antigenic determinants during spermatogenesis. MAFA did not react with oesophagus, stomach, duodenum, ileum, nasal lining tissues, uterus, pericardium, pancreas, thyroid gland, or cultured fibroblasts. The xenoantisera did, however stain the skin epidermis and cultured keratinocytes which exhibited filamentous cytoplasmic staining although their target antigens could not be biochemically identified. These results indicate that the FS proteins express antigenic determinants which are not shared with other cytoskeletal elements within the sperm flagellum or a variety of somatic tissues.

AJ-p90: a novel protein of the perinuclear theca in human sperm subacrosome

A perinuclear theca protein of the human sperm subacrosome was detected using LH43 monoclonal antibody which was originally raised against human keratinocytes. Using indirect immunofluorescence, the antibody stained the acrosomal zone (AZ) of dried ejaculated spermatozoa but did not react with viable cells, thus suggesting that the antigen was intracellular. This was confirmed by immunogold electron microscopy which also revealed the ultrastructural localisation of the antigen to the subacrosomal fibrils. Throughout spermatogenesis the antigen was only detected on the AZ of developed testicular spermatozoa and its expression was continued during their epididymal passage. Biochemically, the protein was insoluble in Triton, and dithiothreitol (DTT) was required for its solubilisation. In Western blotting of sperm and keratinocyte lysates, the antibody detected similar 90-kDa protein doublets (AJ-p90). These biochemical features exclude the identity of AJ-p90 with various cyto- and karyo-skeletal antigens, including the intermediate filaments and microfilaments. AJ-p90 therefore represents a novel product of the subacrosomal perinuclear theca. The significance of these data is discussed together with the importance of the antibody for probing the perinuclear theca in normal and abnormal germ cells, including multinucleated spermatids which also showed reactivity with the antibody.

Detection of a novel basement membrane antigen by GDA-J/F3 anti-human sperm fibrous sheath monoclonal antibody

Basement membrane zones (BMZ) of human epithelia were stained with GDA-J/F3 monoclonal antibody, which was originally raised against sperm cells. Using indirect immunofluorescence and immunoperoxidase techniques, the antibody reacted with the BMZ of stratified squamous epithelia (skin and its appendages, tongue, lip, oesophagus and cervix). It also stained the BMZ of trachea, nasal ciliated mucosa, some mammary ducts of lactating and resting breast, amnion and ureter but failed to react with that of stomach, ileum, colon, rectum, kidney, liver, fallopian tube, lung or their blood vessels. In testes, the antibody did not react with the BMZ of the seminiferous tubules although the sperm tails were stained. Split-skin immunofluorescence and immunoelectron microscopy localized GDA-J/F3 antigen to the inferior border of the lamina densa of the BMZ. In human foetuses, the epidermally associated antigen was detected at an estimated gestational age of 9 weeks, and in the amnion at 15 weeks. The antibody reacted with tissues from monkey but not from mouse, rat, cow or pig suggesting the late appearance of the antigen during evolution. Although the GDA-J/F3 was difficult to characterize biochemically, its tissue distribution, ontogeny and ultrastructural localization suggests that this antigen may be a type VII collagen-associated protein, whose expression is altered in recessive dystrophic epidermolysis bullosa. This disease could represent abnormalities in type VII collagen structure, assembly, transport or interaction with associated proteins.

AJ-p97: a novel antigen of the human sperm tail fibrous sheath detected by a neurofilament monoclonal antibody

Using indirect immunofluorescence (IIF), the RT97 anti-neurofilament monoclonal antibody (MoAb) detected an intracellular antigen in the principal piece of human ejaculated sperm tails. Its localisation to the tail fibrous sheath (FS) was confirmed by immunoelectron microscopy (IEM), which showed the binding of the gold particles to the outer FS surface. During spermatogenesis the antigen was first expressed on the spermatid FS, and its expression was continued on ejaculated mature sperm. In Western blotting of sperm lysates, the RT97 reacted with a 97 kDa protein (AJ-p97) which lacked disulphide bonds. This antigen was not detected on mouse or rat sperm tail FS, suggesting a sequence divergence of the AJ-p97 during evolution. The significance of these results and the relationship of AJ-p97 to neurofilaments are discussed, together with the use of the antibody as a probe for the structural dissection of the FS and for analysing the molecular events that take place during spermiogenesis, especially those involved in sperm tail morphogenesis.

GDA-J/F7 monoclonal antibody: a new marker for sperm cell precursors in human semen

Germ cells isolated from semen of oligospermic human donors were found to react with GDA-J/F7 monoclonal antibody (MoAb). Their reactions with this antibody were demonstrated by using fluorescein activated cell sorter (FACS) analysis and indirect immunofluorescence (IIF) test. In the IIF test, the MoAb recognised an antigen on the surface of the sperm cell precursors (SpP) as well as on mature spermatozoa. The specificity of the antibody reaction with the SpP was further confirmed by immunoelectron microscopy. The MoAb did not react with peripheral blood lymphocytes or polymorphonuclear cells but did show cross-reactivity with monocytes. This antibody therefore provides the first marker for the SpP and could be used as a probe for their distinction from leucocytes. This could have clinical application in seminal analysis.

Analysis of HLA antigens on germ cells in human semen

Nucleated cells other than sperm (NCOS) were isolated from human semen by centrifugation on a Ficoll density gradient. Using tissue-specific monoclonal antibodies (mAb) greater than 99% of the NCOS were found to be sperm cell precursors (SpP). These cells were tested for the expression of class I and II (DR, DP and DQ) HLA antigens by using specific mAb. The anti-HLA class I and II and anti-beta 2-microglobulin mAb reacted with less than 1% of the NCOS. This was demonstrated by indirect immunofluorescence microscopy and fluorescence-activated cell sorter analysis. These results were similar to those obtained from testing germ cells in frozen sections of normal adult testis using the same panel of mAb. In mixed lymphocyte-NCOS cultures, the SpP failed to stimulate allogeneic lymphocytes even when different concentrations of cells were used. These results indicate little or no expression of HLA class I and II including the HLA-D (T cell-defined) determinant on the SpP, a phenomenon which could be of biological importance.