Age related carbohydrate content of mouse kidney glomerular basement membrane and its reactivity to antistreptococcal membrane antisera

Epitope mapping of homologous and cross-reactive antigens by monoclonal antibodies to streptococcal cell membrane (mAb to SCM)

An approach to epitope mapping of a series of anti-streptococcal cell membrane (SCM) mAbs is described. Evaluations by enzyme-linked immunosorbent assay (ELISA) of one control mAb HB-35 and 13 different anti-SCM mAbs were made on homologous SCM antigen and human basement membrane antigens isolated from glomeruli (GBM) and lung (LBM). These anti-SCM mAbs were previously shown to be cross-reactive in a variety of systems with both GBM and LBM. The binding capacities were measured for all 14 mAbs on ELISA plates sensitized with SCM antigen or the cross-reactive GBM or LBM antigens, at 5 micrograms/ml or approximately 20 pM/well. From the 50% binding capacity dilution the pM of mAb bound/pM antigen-well was calculated which translated into an estimate of the ratio-number of epitopes bound. Observations with the homologous and cross-reactive antigens showed multiple reactive epitope ratios to eight mAbs whereas the other five yielded a ratio value of one or two on the tested antigens. Plates blocked with a specific dilution of one mAb evaluated the binding by a second mAb providing both binding and specificity data. One mAb (I-F-3) blocked all the other anti-SCM mAbs on all three antigen plates. An additive effect was noted by three mAbs, I-G-8, II-C-4 and II-D-8 with most of the other mAbs. The order of placement, however, made distinctive differences; II-F-4 showed an additive or enhancement effect on I-B-5 but no reciprocal effect was seen. A similar effect was made with I-G-8 and II-C-4 or I-F-7. Possible interpretations are that each mAb is binding different epitopes each fully exposed, and the order of placement of the mAbs makes no difference. Where an enhanced effect was observed it is suggested that the binding of the first mAb changed the conformation of the antigen, thereby opening and exposing additional epitope(s) to the second antibody. Or, in contrast, where the second mAb was blocked by the first, a fixing of the protein conformation is suggested thereby occluding the other epitope, as seen with I-F-3 and II-C-4. These epitope mapping procedures confirmed that all 13 anti-SCM mAbs were binding at different epitopes. The nature of basement membrane collagens and how this relates to post-streptococcal sequelae will be discussed.

Immunochemical studies of streptococcal cell membrane antigens immunologically related to glomerular basement membrane

Pursuing an autoimmune model for the etiology of poststreptococcal glomerulonephritis, protein antigens isolated from the cytoplasmic membrane of nephritogenic group A Type 12 Streptococcus pyogenes were immunochemically characterized using antistreptococcal cell membrane (SCM) monoclonal antibody (MAb) cross-reactive with glomerular basement membrane (GBM). Low molecular weight (9.2, 7.0, 4.7, 2.3 kDa) HPLC-purified SCM polypeptide antigens were characterized by competitive inhibition and equilibrium dialysis. Competitive inhibition of the MAb, by different sized SCM polypeptide antigens showed an inverse relationship between the size of these antigens and the molar amount required to obtain 50% inhibition of the MAb, confirming previous observations that suggested that these SCM antigens exhibit increasing epitope concentration with increasing size, that is constant epitope density. The observed changes in epitope concentration correlated with differences in the valence and affinity of the MAb as determined by equilibrium dialysis. The Kds of the MAb for 9.2-, 7.0-, 4.7-, and 2.3-kDa SCM antigens ranged from 7.42 x 10(-7) to 1.15 x 10(-5). The experimentally determined MAb valence for these antigens was 2 for the 9.2-kDa antigen and approached 10 for the smaller antigens. Finally, the similarity of these SCM antigens was reflected in similar amino acid compositions; of note, these data agreed with the compositions previously reported for sized GBM antigens. Concentrations of Asp, Thr, Ser, Glu, Gly, Ala, Val, Ile, and Leu paralleled increasing epitope concentration. Apparent N-terminal blocking prevented sequencing of these peptides, but these immunochemical data suggest that intact SCM antigen recognized by the anti-SCM MAb consists of repeating epitopes, an observation consistent with the cytoplasmic membrane source of the antigen.

Localization of [14C] labeled anti-streptococcal cell membrane monoclonal antibodies (anti-SCM mAb) in mice

Six different hybridomas secreting anti-SCM mAb and one control mAb were placed into adult mice along with [14C] amino acids for biosynthetically labeling. After sacrifice, the 14C mAb ascites along with serum, heart, kidney, lung and skeletal muscle were recovered. Tissue associated specific radio-activity (SpAc) and microscopic structural analyses were performed. Confirmation of mAb specificity was by both immunodot blots as well as Western blot analysis. Peritoneal injection of measured doses of anti-SCM mAb yielded tissue SpAc confirming their in vitro specificities. Two of the mAb showed strong reactivity to both renal (GBM) and lung basement membrane (LBM), two were mainly GBM reactive and two showed polyreactivity with a marked reactivity to a Z-line antigen. Autoradiographic light microscopy confirmed that the anti-SCM mAbs bound to both GBM and LBM and to Z-line antigen. Titrated doses of the mAb yielded autoradiographic confirmation in which the grain number on the GBM and LBM increased with increasing dose of mAb for all mAb except the control. This effect was not seen in the muscle tissues but anatomical localization at the Z-line was consistent. The major significance of these studies is the demonstration that circulating antibodies to SCM can react in vivo with normal mammalian antigens adding confirmation to the in vitro specificity of these cross-reactive anti-SCM mAbs.

Chemical composition and solubility of human glomerular and tubular basement membranes of adult and senescent men

The effect of aging on the composition of human renal basement membranes was studied in persons aged 22-90 years. The relative proportion of cortex in kidney appears to decrease with aging. Twenty pairs of GBM and TBM preparations were isolated using the detergent method. Protein content of the basement membrane preparations amounts to about 66% and is independent of type of membrane or age. Amino acid and carbohydrate analyses of both GBM and TBM revealed that the extents of hydroxylation of proline at the C4 position and of lysine decrease with aging. In the case of lysine this occurred from the seventh of life onwards. The decreases are probably not caused by a change of the collagen content. The extent of glycosylation of hydroxylysine is similar for all basement membrane preparations. An adapted protein assay is presented for solutions containing SDS and dithiothreitol. In the presence of these two compounds, solubility of GBM and TBM from adult and aged persons is similar and amounts to about 55 and 85% after 10 and 60 min, respectively, of heating at 95 degrees C. In SDS-polyacrylamide gels, no differences were observed for the major peptide bands between the preparations, irrespective of basement membrane type or age.

The immunomodulatory effect of anti-Micrococcus luteus antibodies. I. Effect on in vitro rabbit T cell functions

A range of purified rabbit anti-Micrococcus luteus antibodies (anti-MCAb) were tested for their ability to interfere with a variety of in vitro immune responses. Such antibodies strongly inhibited the secondary IgG antibody response to sheep red blood cells without affecting the IgM response or the proliferative responses to mitogens and antigens. By exposing lymphocyte populations to anti-MCAb, it was found that such reagents exerted a strong mitogenic effect on rabbit T lymphocytes, provided these cells were derived from antigen-activated lymph nodes. This mitogenic effect was also obtained with F(ab')2 fragments of anti-MCAb and with hybridoma-derived anti-MCAb. Collectively, these data indicate that anti-MCAb inhibit the initiation of IgG synthesis possibly through the expansion of immunoregulatory T cell subsets.

Chemical characterization of glomerular and tubular basement membranes of men of different age

Pairs of glomerular and tubular basement membrane preparations were obtained from kidneys of individuals of premature age up to 80 years. The purity of the preparations was established with light and electron microscopy and by estimating the total phosphorus content. The amino acid and carbohydrate composition was determined and statistically evaluated for 33 to 38 preparations divided over five age groups. Comparison of glomerular and tubular basement membranes from the same kidneys showed that regardless of age glomerular basement membranes contain more 3-hydroxyproline and more of the heteropolysaccharide constituents neuraminic acids and mannose. These differences cannot be ascribed solely to the presence of a minor amount of interstitial collagen. The chemical composition of the two types of basement membranes changes with age. For the first few years after birth the contents of glycine and total imino acids increase and those of collagen-nonspecific amino acids decrease, whereas constituents of the heteropolysaccharide units do not change markedly. These results suggest that proportions of collagenous and noncollagenous peptide moieties gradually change with age in both glomerular and tubular basement membranes. In addition, the extent of hydroxylation of proline and lysine increases significantly with age, reaching an adult level for glomerular basement membranes after 4 to 7 months of age and for tubular basement membranes during late childhood. The contents of glucose and galactose rise with age to an extent comparable with that of hydroxylysine. The age-related changes in basement membrane composition may influence functional properties of these extracellular renal structures.

Chemical characterization of glomerular and tubular basement membranes of cattle of different ages

Glomerular and tubular basement membranes were isolated from fetal, neonatal, young and adult bovine kidneys. An isolation method with sieves for both glomeruli and tubules from the same kidney was developed. A detergent procedure appeared to give purer glomerular and tubular basement membrane preparations than the generally used sonication method. No large differences were found in the composition of glomerular and tubular basement membrane of adult animals. Glomerular and tubular basement membrane preparations of the four age groups showed an increase with age of hydroxylysine and both 3- and 4-hydroxyproline. The most marked increases appeared at different stages of development, that of tubular basement membrane being between fetal and neonatal stages and glomerular basement membrane between 18 weeks old and adult animals. The ratio of 3- to 4-hydroxyproline increased considerably during development. Total imino acid content was higher for both types of basement membrane from adult than from young animals, while total content of hydroxylysine plus lysine remained fairly constant. The increase in hydroxylation of lysine was accompanied by a corresponding change in glucose and galactose content so that the ratio of galactose to hydroxylysine or glucose to galactose remained constant. Fucose content of both types of basement membranes was the same for all age groups but content of aminosugars and mannose gradually increased with age.

Cellular reactivity to altered glomerular basement membrane in glomerulonephritis

Glomerular basement membrane may be altered during glomerulonephritis, exposing antigens that are recognized as foreign. Immunochemical studies suggest that removal of peripheral glycopeptides from the basement membrane with glycosidase mimics this pathogenetic event. To examine these hypotheses, we studied 24 patients with biopsy-proved glomerulonephritis by means of the lymphocyte-blast-transformation assay. Three preparations of normal glomerular basement membrane were used: two mimicked the native state for the peripheral glycopeptides, and one was altered by glycosidases. Results showed minimal differences in responses to native glomerular basement-membrane preparations among patients with glomerulonephritis and control groups. However, patients with glomerulonephritis had a significant blastogenic response to the glycosidase-treated glomerular basement membrane as compared to patients with nonglomerular renal disease and normal controls (P less than 0.0005). These studies suggest that cellular reactivity to altered glomerular basement-membrane antigens can be detected in certain forms of progressive glomerulonephritis.