Low Vitamin-D Levels Combined with PKP3-SIGIRR-TMEM16J Host Variants Is Associated with Tuberculosis and Death in HIV-Infected and -Exposed Infants

Background

This study examined the associations of 25-hydroxyvitamin D and specific host genetic variants that affect vitamin D levels or its effects on immune function, with the risk of TB or mortality in children.

Methods

A case-cohort sample of 466 South African infants enrolled in P1041 trial (NCT00080119) underwent 25-hydroxyvitamin D testing by chemiluminescent immunoassay. Single nucleotide polymorphisms (SNPs) that alter the effect of vitamin D [e.g. vitamin D receptor (VDR)], vitamin D levels [e.g. vitamin D binding protein (VDBP)], or toll like receptor (TLR) expression (SIGIRR including adjacent genes PKP3 and TMEM16J) were identified by real-time PCR. Outcomes were time to TB, and to the composite of TB or death by 192 weeks of follow-up. Effect modification between vitamin D status and SNPs for outcomes was assessed.

Findings

Median age at 25-hydroxyvitamin D determination was 8 months; 11% were breastfed, 51% were HIV-infected and 26% had low 25-hydroxyvitamin D (<32ng/mL). By 192 weeks, 138 incident TB cases (43 definite/probable, and 95 possible) and 26 deaths occurred. Adjusting for HIV status and potential confounders, low 25-hydroxyvitamin D was associated with any TB (adjusted hazard ratio [aHR] 1.76, 95% CI 1.01–3.05; p = 0.046) and any TB or death (aHR 1.76, 95% CI 1.03–3.00; p = 0.038). Children with low 25-hydroxyvitamin D and TMEM 16J rs7111432-AA or PKP3 rs10902158-GG were at increased risk for probable/definite TB or death (aHR 8.12 and 4.83, p<0.05) and any TB or death (aHR 4.78 and 3.26, p<0.005) respectively; SNPs in VDBP, VDR, and vitamin D precursor or hydroxylation genes were not. There was significant interaction between low 25-hydroxyvitamin D and, TMEM 16J rs7111432-AA (p = 0.04) and PKP3 rs10902158-GG (p = 0.02) SNPs.

Conclusions

Two novel SNPs, thought to be associated with innate immunity, in combination with low vitamin D levels were identified as increasing a young child’s risk of developing TB disease or death. Identifying high-risk children and providing targeted interventions such as vitamin D supplementation may be beneficial.

Trial Registration

ClinicalTrials.gov NCT00080119

Behind the scenes of vitamin D binding protein: more than vitamin D binding

Although being discovered in 1959, the number of published papers in recent years reveals that vitamin D binding protein (DBP), a member of the albuminoid superfamily, is a hot research topic. Besides the three major phenotypes (DBP1F, DBP1S and DBP2), more than 120 unique variants have been described of this polymorphic protein. The presence of DBP has been demonstrated in different body fluids (serum, urine, breast milk, ascitic fluid, cerebrospinal fluid, saliva and seminal fluid) and organs (brain, heart, lungs, kidneys, placenta, spleen, testes and uterus). Although the major function is binding, solubilization and transport of vitamin D and its metabolites, the name of this glycoprotein hides numerous other important biological functions. In this review, we will focus on the analytical aspects of the determination of DBP and discuss in detail the multifunctional capacity [actin scavenging, binding of fatty acids, chemotaxis, binding of endotoxins, influence on T cell response and influence of vitamin D binding protein-macrophage activating factor (DBP-MAF) on bone metabolism and cancer] of this abundant plasma protein.

Degalactosylated/Desialylated Bovine Colostrum Induces Macrophage Phagocytic Activity Independently of Inflammatory Cytokine Production

BACKGROUND/AIM

Colostrum contains antibodies, such as immunoglobulin G (IgG), immunoglobulin A (IgA) and immunoglobulin M (IgM), and, therefore, has potent immunomodulating activity. In particular, IgA has an O-linked sugar chain similar to that in the group-specific component (Gc) protein, a precursor of the Gc protein-derived macrophage-activating factor (GcMAF). In the present study, we investigated the macrophage-activating effects of degalactosylated/desialylated bovine colostrum.

RESULTS

We detected the positive band in degalactosylated/ desialylated bovine colostrum by western blotting using Helix pomatia agglutinin lectin. We also found that degalactosylated/ desialylated bovine colostrum could significantly enhance the phagocytic activity of mouse peritoneal macrophages in vitro and of intestinal macrophages in vivo. Besides, degalactosylated/desialylated bovine colostrum did not mediate the production of inflammatory cytokines such as tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β).

CONCLUSION

Similar to the use of GcMAF, degalactosylated/desialylated bovine colostrum can be used as a potential macrophage activator for various immunotherapies.

Gc protein (vitamin D-binding protein): Gc genotyping and GcMAF precursor activity

The Gc protein (human group-specific component (Gc), a vitamin D-binding protein or Gc globulin), has important physiological functions that include involvement in vitamin D transport and storage, scavenging of extracellular G-actin, enhancement of the chemotactic activity of C5a for neutrophils in inflammation and macrophage activation (mediated by a GalNAc-modified Gc protein (GcMAF)). In this review, the structure and function of the Gc protein is focused on especially with regard to Gc genotyping and GcMAF precursor activity. A discussion of the research strategy "GcMAF as a target for drug discovery" is included, based on our own research.

Therapeutic potential of vitamin D-binding protein

Vitamin D-binding protein (DBP) is a multi-functional plasma protein with many important functions. These include transport of vitamin D metabolites, control of bone development, binding of fatty acids, sequestration of actin and a range of less-defined roles in modulating immune and inflammatory responses. Exploitation of the unique properties of DBP could enable the development of important therapeutic agents for the treatment of a variety of diseases.

Measurement of vitamin D-binding protein in pleural fluids and sera by means of a turbidimetric immunoassay measuring system

BACKGROUND

Vitamin D-binding protein (DBP) has been recognized as a multifunctional plasma protein that can modulate certain immune and inflammatory responses. There may be differences between the DBP concentrations in pleural fluids from various diseases involving a variety of possible responses in the pleural cavity.

METHODS

An anti-DBP polyclonal antibody was prepared using commercially available DBP to establish a quantitative measuring system for DBP. With a rabbit antibody, a turbidimetric immunoassay (TIA) was developed for DBP with an automatic analyzer. Using this measuring system, the concentrations of DBP were compared with the protein concentration in pleural fluid and serum specimens from patients with various diseases.

RESULTS

The fluid DBP concentrations in transudative (n=11) and exudative (n=41) effusions were 71.9+/-21.2 and 180.7+/-43.7 mg/l, respectively. Among the exudative effusions, the fluid DBP concentrations in the bacterial (n=10), tuberculous (n=13), and malignant (n=18) effusions were 218.8+/-37.3, 186.7+/-26.2, and 155.1+/-41.3 mg/l, respectively. The DBP fluid/serum ratio and the fluid DBP/protein ratio in bacterial effusions were significantly higher than those in tuberculous (p<0.005, p<0.05, respectively) and malignant effusions (p<0.0005, p<0.005, respectively), although no statistically significant differences in the serum DBP/protein ratio between those effusions were found.

CONCLUSIONS

Using the TIA assay, the DBP concentrations in bacterial pleural effusions were significantly higher than in tuberculous and malignant effusions.

Characterization of 25-hydroxyvitamin D binding protein from intestinal cells

We have previously purified a cytosolic vitamin D metabolite binding protein (cDBP) from rat enterocytes, which has characteristics distinct from other vitamin D binding proteins. In these studies, we demonstrate that cDBP in a semi-purified fraction from human intestinal cells (Caco-2 cells) binds 25-hydroxyvitamin D (25OHD) with at least a 1000-fold greater affinity than 1, 25-dihydroxyvitamin D (1,25(OH)(2)D) or 24,25-dihydroxyvitamin D. Treatment of cells with 1,25(OH)(2)D reduced 25OHD binding to approximately one third that of the untreated cells (0.42 CPM/mg total protein vs 1.34 CPM/mg total protein, respectively). Finally, the cDBP is not immunoreactive to antibodies prepared against the C-terminus of the nuclear vitamin D receptor (VDR). In summary, cDBP bound 25OHD with greater affinity than either 1,25(OH)(2)D or 24,25 dihydroxyvitamin D, the cytosolic binding activity was down-regulated by 1,25(OH)(2)D and cBDP is distinct from the nuclear VDR.

Structurally well-defined macrophage activating factor derived from vitamin D3-binding protein has a potent adjuvant activity for immunization

Freund's adjuvant produced severe inflammation that augments development of antibodies. Thus, mixed administration of antigens with adjuvant was not required as long as inflammation was induced in the hosts. Since macrophage activation for phagocytosis and antigen processing is the first step of antibody development, inflammation-primed macrophage activation plays a major role in immune development. Therefore, macrophage activating factor should act as an adjuvant for immunization. The inflammation-primed macrophage activation process is the major macrophage activating cascade that requires participation of serum vitamin D3-binding protein (DBP; human DBP is known as Gc protein) and glycosidases of B and T lymphocytes. Stepwise incubation of Gc protein with immobilized beta-galactosidase and sialidase efficiently generated the most potent macrophage activating factor (designated GcMAF) we have ever encountered. Administration of GcMAF (20 or 100 pg/mouse) resulted in stimulation of the progenitor cells for extensive mitogenesis and activation of macrophages. Administration of GcMAF (100 pg/mouse) along with immunization of mice with sheep red blood cells (SRBC) produced a large number of anti-SRBC antibody secreting splenic cells in 2-4 days. Thus, GcMAF has a potent adjuvant activity for immunization. Although malignant tumours are poorly immunogenic, 4 days after GcMAF-primed immunization of mice with heat-killed Ehrlich ascites tumour cells, the ascites tumour was no longer transplantable in these mice.

Epitope analysis of monoclonal antibodies to human Gc globulin (vitamin D-binding protein)

Gc globulin, also called vitamin D-binding protein, is a human 56 kDa plasma protein. Antigenic epitopes of the protein recognized by 12 different monoclonal antibodies (MoAbs), including the previously prepared MoAb E12 of which binding to Gc is inhibited by actin, were analyzed in relation to the functional domains of the protein. To map the epitopes recognized by the respective antibody, the reactivities of the MoAbs were tested by immunoblotting against the recombinant Gc fragments expressed in E. coli cells, and then a competitive ELISA was performed. The results showed that the antibodies were classified into at least six groups. Furthermore, in addition to E12, actin inhibited the reactivity of MoAb 21, of which the epitope was located within residues Asp320 to Glu379, in an ELISA in the presence of the ligand. This result must indicate that this antibody-binding site is near the site that interacts with actin. In contrast, no inhibitory effect by 25-hydroxyvitamin D to any antibodies was observed. Furthermore, all antibodies, including E12 and 21, reacted with membrane-bound Gc of lymphocytes by an immunofluorescence study, suggesting that Gc is unlikely to bind to the plasma membrane in its interaction with actin.

Bacterial expression of human vitamin D-binding protein (Gc2) in functional form

In this report, we report the first expression of human vitamin D-binding protein (hDBP), a serum protein with several functions and a multidomained structure, in Escherichia coli. The recombinant protein (reDBP) was expressed as a fusion partner of glutathione S-transferase in order to facilitate proper folding of the reDBP; E. coli-expressed DBP was found to be fully functional with respect to vitamin D sterol binding, interaction with actin, and cross-reactivity with anti-DBP antibody. Furthermore, both natural DBP and reDBP were affinity-labeled with 25-hydroxyvitamin D3-3-bromo[1-14C]acetate in a similar fashion. Availability of an expression system for hDBP in functional form provides opportunity to develop mutants and truncated DBPs to study multiple ligand-binding properties of this protein in relationship with its structure.

Deglycosylation of serum vitamin D3-binding protein by alpha-N-acetylgalactosaminidase detected in the plasma of patients with systemic lupus erythematosus

A serum glycoprotein, Gc protein (vitamin D3-binding protein), can be converted by beta-galactosidase of B cells and sialidase of T cells to a potent macrophage-activating factor (MAF), a protein with N-acetylgalactosamine as the remaining sugar moiety. Thus, Gc protein is the precursor for MAF. Treatment of Gc protein with immobilized beta-galactosidase and sialidase generates a remarkably high titered macrophage-activating factor (GcMAF). When peripheral blood monocytes/ macrophages (designated macrophages) of 33 systemic lupus erythematosus patients were incubated with GcMAF (100 pg/ml), the macrophages of all patients were activated as determined by superoxide generation. However, the precursor activity of patient plasma Gc protein was lost or reduced in these patients. Loss of the precursor activity was the result of deglycosylation of plasma Gc protein by alpha-N-acetylgalactosaminidase activity found in the patient plasma. Levels of plasma alpha-N-acetylgalactosaminidase activity in individual patients had an inverse correlation with the MAF precursor activity of their plasma Gc protein. Deglycosylated Gc protein cannot be converted to macro-phage-activating factor. The resulting defect in macro-phage activation may lead to an inability to clear pathogenic immune complexes. Thus, elevated plasma alpha-N-acetylgalactosaminidase activity resulting in the loss of MAF precursor activity and reduced macro-phage activity may play a role in the pathogenesis of systemic lupus erythematosus.

Vitamin D3-binding protein as a precursor for macrophage activating factor in the inflammation-primed macrophage activation cascade in rats

When rat peritoneal nonadherent cells were treated with inflammatory lipid metabolites and cultured with adherent cells in 1% fetal calf serum (FCS) supplemented medium RPMI 1640 (FCS medium) for 3 hr, markedly enhanced phagocytic and superoxide generating capacities of macrophages were observed. Stepwise preparation of conditioned medium of lysophosphatidylcholine (lyso-Pc)-treated B cells and untreated T cells in FCS medium generated a potent macrophage activating factor whereas cultivation of lyso-Pc-treated B cells alone in a 1% adult rat serum supplemented medium efficiently generated the macrophage activating factor. Generation of macrophage activating factor requires a precursor protein, serum vitamin D3-binding protein (DBP), as well as participation of lymphocyte glycosidases. The lyso-Pc-inducible beta-galactosidase of B lymphocytes and the Neu-1 sialidase of T lymphocytes modified bovine DBP (bDBP) to yield the macrophage activating factor, a protein with N-acetylgalactosamine as the remaining sugar. In contrast, lyso-Pc-inducible beta-galactosidase of B cells alone modified rat DBP (rDBP) to yield the macrophage activating factor, a protein with N-acetylgalactosamine as the remaining sugar. Thus, we conclude that bDBP carries a trisaccharide composed of N-acetylgalactosamine, galactose, and sialic acid while rDBP carries a disaccharide composed of N-acetylgalactosamine and galactose.

Roles of beta-galactosidase of B lymphocytes and sialidase of T lymphocytes in inflammation-primed activation of macrophages

The outer surface of mouse B lymphocytes carries constitutive and inducible beta-galactosidase isozymes. A brief (30 min) treatment of B lymphocytes with lysophosphatidylcholine (lyso-Pc) immediately induced an approximate 3-fold higher beta-galactosidase activity than the constitutive isozyme of untreated B lymphocytes. Thus, the lyso-Pc-inducible isozyme is not a de novo enzyme. Outer surface of mouse T lymphocytes carries constitutive (non-Neu-1) and inducible (Neu-1) sialidase isozymes. The lyso-Pc-inducible beta-galactosidase of B lymphocytes and the Neu-1 sialidase of T lymphocytes were required for conversion of vitamin D3-binding protein (Gc protein) to a potent macrophage activating factor. This enzymatic generation of the macrophage activating factor was mediated via enzyme-associated receptors.

Human testis vitamin D binding protein involved in infertility

Immunoglobulin G (IgG) fraction was prepared from a serum obtained from an infertile woman containing antisperm antibodies that induced head-to-head agglutination of human sperm. The antibodies in the IgG fraction interacted with a 60-kD protein found in human testes determined by Western blot. The 60-kD protein was purified from human testis by isoelectric focusing (IEF), affinity chromatography on blue sepharose column, and preparative electrophoresis with electroelution. The purified 60-kD protein migrated as a single homogeneous band when analyzed by SDS-PAGE. The amino acid sequence of the N-terminus was determined. The initial 10 amino acid residues were identical to the human serum vitamin D binding protein (VDBP). Polyclonal antibodies were raised against the 60-kD protein. The polyclonal anti-60-kD antibodies and the anti-VDBP antibodies obtained from a commercial source immobilized human sperm in vitro. The interacting antigens were located on the postacrosomal region and midpiece of human sperm, as determined by an immunofluorescence method. The IgG fraction prepared from the serum of an infertile woman interacted with the human testis 60-kD protein but failed to stain serum VDBP. The results suggest that the 60-kD and VDBP are related proteins but not identical entities and that the 60-kD protein contains a unique structural group lacking in serum VDBP. Production of antibodies against the unique structure of the 60-kD protein may be the cause of the infertility.

Human monocyte chemotaxis to complement-derived chemotaxins is enhanced by Gc-globulin

Gc-globulin has been found in bronchoalveolar lavage fluid in patients with chronic obstructive pulmonary disease (COPD) and adult respiratory distress syndrome (ARDS) and has been shown to enhance neutrophil chemotaxis to C5-derived peptides in vitro. We proposed that Gc-globulin may enhance the inflammatory response in lungs by influencing monocyte chemotaxis to C5-derived peptides as it does with neutrophils. Monocyte chemotaxis was measured in blind well chambers by a leading-front technique. Purified human Gc-globulin had no intrinsic chemotactic activity for monocytes at concentrations ranging from 1 fM to 1 microM. However, Gc-globulin, at concentrations as low as 10 pM, increased monocyte chemotaxis over 10-fold in a concentration-dependent fashion when added to non-chemotactic doses of C5a (0.1 nM) and C5a des Arg (0.5 nM). The chemotaxis-enhancing effect of Gc-globulin was specific for C5-derived peptides, as Gc-globulin did not enhance monocyte chemotaxis to other chemoattractants such as leukotriene B4 or formyl-Met-Leu-Phe. The enhancement of monocyte chemotaxis to C5-derived peptides by Gc-globulin was not a nonspecific effect of anionic proteins, as other serum proteins of similar size and charge did not enhance monocyte chemotaxis to C5a des Arg. These results indicate that Gc-globulin enhances the monocyte response to C5-derived peptides and, together with previous work, indicates that its presence in the airways of patients with COPD and ARDS may up-regulate the monocyte inflammatory response in the lungs.

Regulation of inflammation-primed activation of macrophages by two serum factors, vitamin D3-binding protein and albumin

A very small amount (0.0005 to 0.001%) of an ammonium sulfate [50% saturated (NH4)2SO4]-precipitable protein fraction of alpha 2-globulin efficiently supported inflammation-primed activation of macrophages. This fraction contains vitamin D3-binding protein essential for macrophage activation. Comparative macrophage activation studies with fetal calf serum, alpha 2-globulin fraction, 50% (NH4)2SO4 precipitate, and purified bovine vitamin D3-binding protein revealed that fetal calf serum and alpha 2-globulin fraction appear to contain an inhibitor for macrophage activation while ammonium sulfate precipitate contains no inhibitor. This inhibitor was found to be serum albumin. When bovine serum albumin (25 micrograms/ml) was added to a medium supplemented with 0.0005 to 0.05% (NH4)2SO4 precipitate or 1 to 10 ng of vitamin D3-binding protein per ml, activation of macrophages was inhibited.

Vitamin D-binding protein (group-specific component) is the sole serum protein required for macrophage activation after treatment of peritoneal cells with lysophosphatidylcholine

In vitro treatment of mouse peritoneal cells with 1 micrograms lysophosphatidylcholine (lyso-Pc)/mL in serum free-0.1% egg albumin-supplemented RPMI 1640 medium for 30 min, followed by 3 h cultivation in a medium supplemented with human serum, resulted in a greatly enhanced Fc-receptor-mediated phagocytic activity of macrophages. Vitamin D-binding protein (group-specific component [Gc]) of alpha 2-globulin fraction was shown to be the sole serum glycoprotein required for the generation of a potent macrophage-activating factor. When a mixture of lysophosphatidylcholine (lyso-Pc)-treated nonadherent and adherent cells were cultured in a medium supplemented with a small amount of purified Gc protein (1 ng/mL), a greatly enhanced activation of macrophages was demonstrated. The generation of macrophage-activating factor from purified Gc protein was far more efficient than that from whole serum, indicating that a serum component is inhibitory to the activation process of macrophages. While three other major serum glycoproteins (alpha 2-macroglobulin, alpha 2-HS-glycoprotein and haptoglobin) were neither stimulatory nor inhibitory to lyso-Pc-primed macrophage activation, serum albumin (competitively with Gc protein) appeared to be inhibitory to the process of macrophage activation.

Localization and quantitation of the vitamin D binding protein (Gc-globulin) in human neutrophils

Plasma-derived vitamin D binding protein (DBP) is an important physiologic regulator of the neutrophil chemotactic response to activated complement. A cell-associated form of DBP has been observed in numerous cell types. We now report that mature, circulating human neutrophils also contain cell-associated DBP. Immunofluorescence studies of normal untreated neutrophils showed the presence of DBP on the cell surface. Western blotting of detergent-soluble neutrophil lysates with a polyclonal anti-DBP showed two major immunoreactive bands, one with an apparent molecular weight of 56 Kd (identical to purified plasma-derived DBP) and a second less prominent band at 12 to 14 Kd. Quantitation of the immunoreactive bands by video densitometry indicated that normal human neutrophils contain 1.5 +/- 0.8 ng DBP/10(6) cells (n = 9). Immunoprecipitation of detergent-soluble lysates with the polyclonal anti-DBP showed only the 56-Kd form by Western blotting. In contrast, a monoclonal anti-DBP immunoprecipitated the 12 to 14 Kd form of DBP from lysates of surface-radioiodinated cells. Western blots of subcellular fractions showed that immunoreactive bands were found in the specific (secondary) granule and plasma-membrane fractions. In addition, pretreatment of neutrophils with 10 nmol/L phorbol myristate acetate (PMA) resulted in approximately a 50% reduction in the amount of DBP in both the specific granule and plasma-membrane fractions. Finally, analysis of the cell-free supernates showed that DBP was spontaneously released into the extracellular milieu: moreover, this release was enhanced if the cells were first stimulated with C5a, formyl-norleucyl-leucyl-phenylalanine (fNLP) or PMA.

Antibodies to dietary antigens in rheumatoid arthritis--possible molecular mimicry mechanism

Antibodies in serum from some patients with rheumatoid arthritis, recognize bovine albumin present in the milk, as determined by immunoprecipitation analysis from 125I-milk extracts. This antigen was also immunoprecipitated from bovine sera. These and ELISA studies showed that BSA is preferentially recognized over other proteins present in the milk. Panel studies demonstrated that although the average reactivity for BSA was high, only one third of the sera tested displayed a reactivity above the mean. The possibility of a molecular mimicry mechanism in RA between this food antigen and other human antigens was investigated. A sequence alignment analysis showed that the residues 141-157 of bovine albumin significantly differed from the corresponding fragment of human albumin, but were highly homologous with human collagen type I, C1q and vitamin D binding protein. In support of the immunogenicity of this fragment, we found that representative RA sera displayed a specific reactivity for a synthetic peptide containing the BSA residues responsible for the homology. Furthermore, most of the epitopes recognized on BSA by the RA sera seem to be conformationally dependent as heat denaturation or reduction followed by alkylation lead to a diminished recognition.

Rat sulfite oxidase antibodies cross-react with two gene family-related proteins: albumin and vitamin D-binding protein

Screening lambda cDNA libraries from rat liver with antibody to native rat liver sulfite oxidase (RLSO) showed cross-reaction with two proteins that belong to the same gene family: serum albumin and vitamin D-binding protein. Antibodies raised against native RLSO or sodium dodecyl sulfate-denatured protein cross-reacted with these proteins by Western blot analysis. The relative effectiveness of RLSO antibody binding was estimated to be 1/5 for rat serum albumin and 1/10 for rat vitamin D-binding protein. This result was not caused by contaminating proteins in the RLSO used for immunization as the RLSO preparation did not react with rat serum albumin antibody. RLSO antibodies, selected for their ability to bind rat serum albumin immobilized on nitrocellulose, recognized both rat serum albumin and RLSO. RLSO antibody, with albumin-reactive antibody removed, still recognized vitamin D-binding protein, suggesting that multiple determinants specific to each protein are involved in the cross-reaction. Comparison of RLSO antibody binding to the rat and human proteins indicated that the determinants were species-specific. cDNA clones identified by screening cDNA libraries with RLSO antibody demonstrated that these determinants reside in the C-terminal domain of these proteins. These results suggest that these proteins contain some common immunological features and may be evolutionarily related.

Vitamin D3 binding protein required for in vitro activation of macrophages after alkylglycerol treatment of mouse peritoneal cells

In vitro treatment of peritoneal cells with dodecylglycerol (DDG) in 10% foetal calf serum (FCS) supplemented medium RPMI-1640 results in a greatly enhanced Fc receptor-mediated phagocytic activity of macrophages. This macrophage activation process requires a serum factor in the alpha 2-globulin fraction. When mouse peritoneal cells were treated with 50 ng DDG/ml in a serum-free 0.1% egg albumin-supplemented medium RPMI-1640 (EA medium) for 30 min and cultured in EA medium containing electrophoretically fractionated alpha 2-globulin for 3 hr, a markedly enhanced activation of macrophages was observed. To improve fractionation of alpha 2-globulin, FCS was first precipitated with 50% saturated ammonium sulphate and then the supernatant electrophoretically fractionated. The resultant alpha 2-globulin fraction was unable to support activation of macrophages. Vitamin D3 binding protein (DBP) of the alpha 2-globulin fraction is known to be precipitable by 50% saturated ammonium sulphate. When human alpha 2-globulin was treated with antiserum against human DBP and used in a medium for cultivation of DDG-treated peritoneal cells, no significant activation of macrophages was observed. Cultivation of DDG-treated peritoneal cells in a medium containing a low concentration of purified human DBP (group specific component, Gc) produced a greatly enhanced ingestion activity of macrophages. Purified human Gc protein, when used in an EA medium for step-wise cultivation of DDG-treated B and untreated T cells, was efficiently converted to a macrophage-activating factor.

Serologic demonstration of the albuminoid nature of the B700 murine melanoma antigen

Limited available evidence indicates that the B700 murine melanoma antigen is related to serum albumin, but potential relationships to other members of the serum albumin protein family have not yet been established. Using specific antibodies raised against each of the members of the albumin family, we have studied cross-reactivity by solid phase enzyme-linked immunosorbent assay and Western immunoblotting. We demonstrate that B700 is serologically cross-reactive to members of the serum albumin family, which includes alpha-fetoprotein and vitamin D binding protein. Therefore, B700 is part of the serum albumin family of proteins, although the mechanism underlying its specific expression by transformed melanocytes remains unknown.

A monoclonal antibody against human vitamin-D-binding protein for the analysis of genetic variation in the group-specific component system (Gc)

We have developed a murine hybridoma cell line that is stable in secreting a monoclonal antibody (hDBP-1) directed against the group-specific component (Gc) molecule. The hDBP-1 is monospecific for Gc and does not crossreact with human albumin, which has 23% of its amino acid residues identical with vitamin-D-binding protein (DBP). The subclass of the antibody is IgG1 for the heavy chain, the light chain being of the kappa type. Isoelectric focusing discloses four major bands for the hDBP-1 with isoelectric points between pH 6.5 and 7.8. Binding to the antigen at different pH values was determined: there is high affinity in the physiological range and no binding at pH 3.5 and lower. In the presence of high salt concentrations, binding was reduced to about 50% at 1.5 M NaCl. The hDBP-1 recognizes the common human Gc types and the Gc of all apes and old world monkeys. No reaction was observed with the Gc of other mammals such as horses, cattle, rats, rabbits, sheep, goats and pigs. By testing hDBP-1 against 77 of the more than 120 known rare human Gc variants, it could be shown that this monoclonal antibody cannot recognize seven of these rare variants and can only poorly recognize nine. The binding site of hDBP-1 to Gc is not related to the binding site of Gc with G-actin: it recognizes Gc, the binary complex between Gc and G-actin, as well as the ternary complex between Gc, G-actin and DNase I. Competition assays with vitamin D3 and Gc in enzyme-linked immunosorbent assay indicate that the epitope of hDBP-1 on the Gc molecule may be related to the vitamin-D3-binding site.

Inhibition of human natural killer activity by antiserum against vitamin D-binding protein, a group-specific component (Gc)

An anti-Gc antiserum (anti-Gc) was prepared by immunizing rabbits with purified Gc, a major vitamin D-binding protein in human serum. Gc is expressed on the surfaces of a small proportion of resting T cells and almost all B cells are natural killer (NK) cells. We investigated the effects of anti-Gc on NK activity of normal peripheral blood lymphocytes. Both anti-Gc and purified IgG isolated from anti-Gc prominently inhibited human NK activity in vitro. Inhibition of anti-Gc was dependent on the concentration of the antiserum employed. Competition assay showed that purified Gc significantly blocked the inhibitory effect of anti-Gc. The inhibition of NK activity in the cells treated with anti-Gc was restored time-dependently by being cultured in anti-Gc free medium. Anti-Gc-treated NK cells retained their capacity to bind to target cells. These findings suggest that mGc is associated with the process of the NK cytolysis on the post-binding cytolytic phase.

Interstitial deletion of the proximal long arm of chromosome 4 associated with father-child incompatibility within the Gc-system: probable reduced gene dosage effect and partial piebald trait

Gc-system typing by isoelectric focusing polyacrylamide gel electrophoresis and quantitative assays were carried out on a patient with a karyotype of 46,XY,del(4)(q12q21.1) and on his parents with normal chromosomes. Although a father-child incompatibility within the Gc-system suggested that its locus is on segment 4q12-13, the serum concentration of vitamin D binding protein in the patient and his father were only about half of that of his mother and control individuals. The possibility of interference of a silent allele in the child could not be excluded. Associated congenital partial leukodermia appeared to be an expression of a partial piebald trait.

Interaction of Gc (vitamin-D binding protein) with membrane of activated natural cytolytic cells

Gc (a vitamin D binding protein) has been speculated to play a role in the function of immune response, yet, it has not been examined for its biological response properties. Therefore, we tried to (a) characterize the appearance of membrane bound Gc (mGc) on non-activated and mitogen activated lymphocytes as well as on Interleukin-2 activated killer cells and (b) examine the role of serum isolated human Gc on human blastogenesis and cytotoxicity (natural killing and lymphokine-activated killing). Our data suggests that activated cells possess a greater number of cells with mGc than non-activated cells and that as a biological response modified we find modulation of blastogenesis and cytotoxicity to be consistently but not very significantly down-regulated. Anti-Gc antibody was observed to significantly inhibit NK activity.

Distribution of group-specific component subtypes in multiple sclerosis

Genetic subtypes of group-specific component (Gc), a protein possibly influencing susceptibility to human immunodeficiency virus infection, were assessed by isoelectric focusing of plasma from 88 patients with multiple sclerosis (MS) and related to frequencies among 3394 control individuals subjected to paternity studies. We found no clear association between MS and frequencies of phenotypes or alleles of Gc protein.

Identification of the C5a des Arg cochemotaxin. Homology with vitamin D-binding protein (group-specific component globulin)

The chemotactic activity of human C5a des Arg is enhanced significantly by an anionic polypeptide (cochemotaxin) in normal human serum and plasma. The cochemotaxin attaches to sialic acid residues within the oligosaccharide chain of native C5a des Arg to form a complex with potent chemotactic activity for human PMN. We investigated the nature of the cochemotaxin and found that vitamin D-binding protein is the putative cochemotaxin. Vitamin D-binding protein enhanced the chemotactic activity of native C5a des Arg, but had no effect on the chemotactic activity of either native C5a or FMLP. Sialic acid prevented both enhancement by vitamin D-binding protein of the chemotactic activity of native C5a des Arg and formation of C5a des Arg-vitamin D-binding protein complexes, detected by molecular sieve chromatography. Furthermore, vitamin D-binding protein and cochemotaxin exhibited identical molecular weights, isoelectric points, antigenic reactivity, and amino acid composition.

Comparative immunological and electrophoretic analysis of Gc protein in sera from various animals

1. On immunodiffusion, using an anti-human Gc antibody, serum Gc in all mammals tested revealed a partial identity with human Gc. 2. The relative cross-reactivities of serum Gc in monkeys, dogs, cats and rats with human Gc antiserum were found to be more than 70% while the serum Gc in other mammals (pigs, cattle, goats and a guinea pig) was less than 50%. 3. Testing, using the isoelectrofocusing method, showed specific patterns of Gc in the mammals. In the sera of cats and cattle, Gc polymorphisms were detected. 4. Neuraminidase treatment affected the isoelectrofocusing Gc patterns of pigs, goats and cattle, whereas those in other mammals remained unchanged.

Characterization of a monoclonal antibody to human serum vitamin D binding protein (Gc globulin): recognition of an epitope hidden in membranes of circulating monocytes

We have developed a murine hybridoma cell line that secretes a monoclonal antibody directed to the serum human vitamin D binding protein (hDBP), a 58,000-dalton alpha-globulin with a high avidity for 25-hydroxycholecalciferol and globular actin. This immunoglobulin G1 kappa-light chain antibody was produced by the fusion of the spleen cells from BALB/c mice, immunized with purified hDBP, with SP2/0-AG4 myeloma cells. The antibody was easily removed from the supernatant of hybridoma cultures or mouse ascites fluid by Protein A affinity chromatography. Apparent serum monospecificity was demonstrated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and isoelectric focusing gels transblotted to nylon membranes and overlayed with purified MAK 89 antibody and radioiodinated Protein A. The affinity of the antibody is high [dissociation constant (Kd) = 2.6 X 10(-11) M]. Parallel displacement of tracer by hDBP and human serum was observed. The sera from various species displaced the hDBP tracer in the following potency: monkey more than cat more than dog more than guinea pig. RIAs for DBP from several species are feasible with this antibody. This antibody does not, in contrast to polyclonal anti-hDBP antiserum, bind to viable monocytes. However, the MAK 89 antibody does bind to the membranes of well washed, fixed, and permeant circulating monocytes. Surface membrane radioiodination of monocytes and immunoprecipitation of the detergent lysates with the antibody demonstrates a protein with molecular weight equivalent to hDBP. The epitope recognized, therefore, appears to be hidden in the viable cells, suggesting an intimate and intricate association of the hDBP and monocyte plasma membrane.

A radiometric immunosorbent assay for the detection of anti-hormone-binding protein antibodies

A radiometric immunosorbent assay (RISA) for the detection of monoclonal antibodies to hormone-binding proteins has been developed. The assay involves incubating hybridoma supernatants in microtiter wells that have been coated with goat anti-mouse IgG antibodies. Any mouse IgG in the test supernatant is thus specifically retained in the wells. Radioactive ligand-binding protein complexes are then incubated in the wells. The presence of anti-binding protein antibodies in the supernatant is indicated by specific retention of radioactive ligand-binding protein complexes in the wells. Crude antigen preparations, such as tissue homogenates, can be used to detect antibodies. The assay is capable of detecting antibody at concentrations 20 ng/ml (approximately 100 pM IgG). The RISA has been used successfully to screen for monoclonal antibodies to the intracellular receptor for 1,25-dihydroxyvitamin D3 and should be useful for the detection of antibodies to ligand-binding proteins in general.

Monoclonal antibodies to human vitamin D-binding protein

Monoclonal antibodies to vitamin D-binding protein isolated from human serum have been produced. The antibodies obtained have been shown to be specific for human vitamin D-binding protein by three independent assays. The antibodies recognize human vitamin D-binding protein specifically in an enzyme-linked immunosorbent assay. Human vitamin D-binding protein is detected specifically in both pure and crude samples by a radiometric immunosorbent assay (RISA) and by an immunoprecipitation assay. The anti-human vitamin D-binding protein antibodies cross-react with monkey and pig vitamin D-binding protein, but not with vitamin D-binding protein from rat, mouse, or chicken, as determined by the RISA and immunoprecipitation assays.