IgG anti-F Research Articles

Natural IgG Anti-F (ab')2 Autoantibody Activity in Children with Autism.

Background: Many and diverse autoimmune abnormalities have been reported in children with autism. Natural autoantibodies (NAAbs) play important immunoregulatory roles in recognition of the immune self. The objective of this study was to examine the presence of NAAbs in the sera of children with autism and across severity subgroups of autistic behavioral impairments. Methods: NAAbs were titrated in sera through an ELISA procedure in 60 low-functioning children with autism and 112 typically developing controls matched for age, sex and puberty. Results: Serum titers of IgG anti-F(ab')2 autoantibodies were significantly lower in children with autism compared to typically developing controls (p < 0.0001), and were significantly negatively associated with autism severity (p = 0.0001). This data appears to be related more specifically to autism than to intellectual disability, given that IgG anti-F(ab')2 levels were significantly negatively correlated with IQ scores in the autism group (p = 0.01). Conclusions: This is the first report in autism of abnormally low natural anti-F(ab')2 autoantibody activity. The findings suggest a dysfunction of self-recognition mechanisms which may play a role in the pathogenesis of autism, especially for the severely affected children. These findings strengthen the hypothesis of an autoimmune process in autism and open the prospect of alternative medical treatment. Further neuroimmunological research is warranted to understand the exact mechanisms underlying this reduced natural IgG anti-F (ab')2 autoantibody activity, and to assess its impact on the pathophysiology and behavioral expression of autism.

Suppression of anti-erythrocyte autoantibody-producing B cells by a physiological IgG-anti-F(ab')2 antibody and escape from suppression by tumour transformation; a model relevant for the pathogenesis of autoimmune haemolytic anaemia.

We showed previously that broadly reactive IgG anti-immunoglobulin autoantibodies produced by rats during the immune response suppress the B cell response. We report here on the effect of a similar human antibody on self-reactive human B cells. IgG anti-F(ab')2 was added to cultures of anti-erythrocyte autoantibody-producing B cells derived from healthy donors. A dose-dependent suppression of the antibody response was obtained (maximum at 1.3 ng IgG/10(6) cells). This effect was competitively inhibited by F(ab')2 gamma. Autoimmune haemolytic anaemia can be caused by chronic monoclonal B cell proliferation. To reproduce this condition in vitro we immortalized B cells with Epstein-Barr virus (EBV) and raised a B cell population with anti-erythrocyte autoantibody activity. These cells were electrically fused with CB-F7 tumour cells and an IgG1 cold-reactive anti-erythrocyte autoantibody-producing B cell line was established. Surprisingly, the tumour cells were not suppressed by IgG anti-F(ab')2. It is known that anti-immunoglobulins selectively suppress antigen-receptor (AgR)-occupied B cells by a Fc gamma-receptor (Fc gamma R)-mediated mechanism. To occupy their AgR, we preincubated the tumour cells with anti-AgR antibody. In spite of this, their susceptibility to suppression was not restored. As shown by rabbit IgG-sensitized ox erythrocyte (EA)-rosetting, this refractoriness was not due to a loss of Fc gamma R. Our experiments delineate a mechanism of peripheral B cell suppression to autoantigens, and show a way of escape from control relevant for the pathogenesis of autoimmune haemolytic anaemia.

Human IgG anti-F(ab′)2 antibodies possess rheumatoid factor activity

Individual preparations of affinity purified anti-F(ab')2 antibodies and anti-Fc antibodies isolated from the sera of patients with rheumatoid arthritis (RA), were examined for reactivity with the Fab and Fc fragments of human IgG. Western blot assays demonstrated specific interaction of affinity-purified anti-Fab antibodies with both Fab and Fc molecules. Approximately one-half of the anti-Fab antibody preparations studied contained IgG antibodies reactive with Fab and Fc fragments in ELISA, suggesting the existence of naturally occurring epibody-like autoantibodies in these patients. Thirteen of 14 affinity-purified anti-Fc antibody preparations contained IgG cross-reactive with Fab molecules in ELISA. Double-adsorption assays on affinity columns demonstrated that a minimum of 14%, and possibly as much as 50%, of the IgG anti-Fab antibodies reacted with the Fc of IgG. Conversely, a minimum of 12%, and possibly as much as 70%, of the IgG anti-Fc antibodies reacted with IgG Fab molecules. Anti-Fab antibodies isolated from non-RA individuals also exhibited anti-Fc reactivity in ELISA, demonstrating the presence of these dual-reactive antibodies in other autoimmune and normal individuals. These studies establish the presence of naturally occurring IgG autoantibodies reactive with both the Fab and Fc fragments of human IgG. Their existence emphasizes the potential of anti-immunoglobulin antibodies to recognize a multiplicity of antigens, possibly including other members of the immunoglobulin supergene family.

Experimental Hypersensitivity Pneumonitis Induced by Fusarium kyushuense in Mice

Experimental Hypersensitivity Pneumonitis Induced by Fusarium kyushuense in Mice: Koichi Harada, et al. Department of Hygiene, Kumamoto University School of Medicine—Arecently described Fusarium species, Fusarium kyushuense, was isolated from dead leaves of egg plant in a greenhouse where a female farmer who developed hypersensitivity pneumonitis (HP) with progressing lung lesions had been working. The freeze dried fungus was exposed to specific pathogen‐free, 6‐week‐old female C57Black/6J mice under light ether anesthesia. Each mouse received 40 pi of the suspended fungal solution by dropping it onto its nostrils in 5 consecutive days a week for 4 wk. The control group received 40 μl of 0.1 M sterilized phosphate buffered saline. The mice were killed on the 4th day after the final exposure. The lung indices increased dose dependently in the fungus exposed mice groups. The specific IgG anti‐Fkyushuense levels in sera of the high dose group were significantly higher than in the control group (P &lt;0.05 by Ryan's multiple comparison test). Histologically, the lungs of both low and high dose groups showed signs of atelectasis with granulomatous lesions containing multinuclear giant cells and activated macrophages. This is the first report that mice developed HP induced by repeated exposure to freeze dried F. kyushuense.

Inverse Association Between IgG–Anti-κ and Antierythrocyte Autoantibodies in Patients With Cold Agglutination

AbstractIt has been known for a long time that IgG–anti-F(ab′)2 antibodies (Abs) are able to suppress the B-cell response. We showed that natural IgG-anti–F(ab′)2 autoantibodies appear in the serum of patients with cold agglutination. If the anti-F(ab′)2 Ab suppresses cold agglutinin (CA)-producing B cells, one would expect an inverse correlation between the titers of these two Abs. Our study confirmed this correlation. Subsequent experiments showed that some anti-F(ab′)2 Abs bind to the hinge region of IgG. It was difficult to explain how this Ab suppresses CA-producing B cells, which are of IgM isotype. Here we show that patients with cold agglutination have an IgG–anti-κ light chain autoantibody in their serum. This is another member of the anti-F(ab′)2 Ab group. Because the vast majority of CAs are IgM-κ Abs, the anti-κ Ab might suppress CA-producing B cells. If this is the case, there should be an inverse association between the titer of anti-κ Ab and CA. In a group of 302 patients, we found that high titers of the anti-κ Ab correlate with low titers of CA and vice versa (P= .009). Interestingly, this association is found only in patients whose disease is caused by noninfectious agents, including mainly B-cell proliferations (P = .0058). Our data show that the inverse correlation is not confined to a particular CA autoantibody specificity. The results are discussed in the light of recent findings showing that anti-IgM Abs may either inactivate or kill tumoral B cells by apoptosis.

Inverse Association Between IgG–Anti-κ and Antierythrocyte Autoantibodies in Patients With Cold Agglutination

It has been known for a long time that IgG–anti-F(ab′)2 antibodies (Abs) are able to suppress the B-cell response. We showed that natural IgG-anti–F(ab′)2 autoantibodies appear in the serum of patients with cold agglutination. If the anti-F(ab′)2 Ab suppresses cold agglutinin (CA)-producing B cells, one would expect an inverse correlation between the titers of these two Abs. Our study confirmed this correlation. Subsequent experiments showed that some anti-F(ab′)2 Abs bind to the hinge region of IgG. It was difficult to explain how this Ab suppresses CA-producing B cells, which are of IgM isotype. Here we show that patients with cold agglutination have an IgG–anti-κ light chain autoantibody in their serum. This is another member of the anti-F(ab′)2 Ab group. Because the vast majority of CAs are IgM-κ Abs, the anti-κ Ab might suppress CA-producing B cells. If this is the case, there should be an inverse association between the titer of anti-κ Ab and CA. In a group of 302 patients, we found that high titers of the anti-κ Ab correlate with low titers of CA and vice versa (P= .009). Interestingly, this association is found only in patients whose disease is caused by noninfectious agents, including mainly B-cell proliferations (P = .0058). Our data show that the inverse correlation is not confined to a particular CA autoantibody specificity. The results are discussed in the light of recent findings showing that anti-IgM Abs may either inactivate or kill tumoral B cells by apoptosis.

Affinity columns containing anti-DNA Id+ human myeloma proteins adsorb human epibodies from intravenous gamma globulin.

To study eluates of intravenous gamma globulin (IVGG) prepared from affinity columns of human cationic IgG myeloma proteins bearing anti-DNA idiotype (Id) markers 16/6, F4, 3I, and 8.12 for possible anti-Id (combining site) blocking activity. Anti-DNA idiotypic antibody activity was studied in 3 preparations of IVGG containing high, medium, and low levels of IgG anti-F(ab')2, and in 4 other commercial IVGG preparations. Affinity-purified IgG anti-DNA (APAD) from systemic lupus erythematosus (SLE) patients was biotinylated, and binding to DNA coated on enzyme-linked immunosorbent assay plates was used to measure anti-DNA antibody activity. IVGG was adsorbed to Sepharose 4B affinity columns linked to a panel of cationic human IgG myeloma proteins positive for anti-DNA Id markers 16/6, F4, 3I, and 8.12. Material adsorbing to such columns was eluted at low pH (2.5) and after neutralization, tested for its ability to inhibit biotinylated APAD reacting with DNA. Only 0.05-0.9% of IVGGs bound firmly to Id affinity columns. These IVGGs were then eluted, using pH 2.5 glycine-saline and eluates neutralized to pH 7.4. Column flowthrough and eluate fractions were compared for their ability to block SLE APAD reacting with DNA. Significant inhibition of SLE APAD combining sites was observed with eluates from anti-DNA Id affinity columns; however, no correlation between IVGG anti-F(ab')2 activity and true anti-Id blocking of APAD was apparent. No residual anti-Id activity remained in column flowthrough fractions. No anti-Id blocking activity was recorded for IVGG eluates from human cationic myeloma columns devoid of the 4 anti-DNA Id markers. DNase treatment of IVGG or Id column eluates did not affect anti-Id blocking activity. Thus, all detectable anti-DNA idiotypic antibody capable of blocking SLE anti-DNA combining sites bound to Id+ affinity columns. Column eluates also showed some relative concentration of IgG anti-DNA activity, which was of lower affinity for DNA than antibodies also present in eluates which blocked anti-DNA combining sites. The presence of both anti-DNA and antiidiotypic (anti-combining site) activity in human anti-DNA Id column eluates indicates that epibodies from IVGG are relatively concentrated when this strategy is used. This approach may lead to a new strategy for treatment of SLE nephritis.

Cross-reactivity of human IgG anti-F(ab')2 antibody with DNA and other nuclear antigens.

To characterize immunologic specificity and possible antiidiotype activity of IgG anti-F(ab')2 in normal subjects as well as in patients with active and inactive systemic lupus erythematosus (SLE). IgG anti-F(ab')2 and anti-double-stranded DNA (anti-dsDNA) were affinity isolated from immunoadsorption columns of F(ab')2 and dsDNA linked to Sepharose 4B. Affinity-purified IgG anti-F(ab')2 (APAF) and affinity-isolated IgG anti-dsDNA (APAD) were tested by enzyme-linked immunosorbent assay (ELISA) for other cross-reacting specificities including anti-Sm, anti-Sm/RNP, and anti- Crithidia binding. Anti-DNA specificity of APAF and APAD was assayed by S1 nuclease treatment of heat-denatured DNA. Rabbit antiidiotypic antisera were prepared by immunization with APAF and APAD from normal subjects and SLE patients and absorption with insolubilized human Cohn fraction II (Fr II). VL and VH regions of 5 monoclonal IgM antibodies with anti-F(ab')2/anti-DNA specificity generated by Epstein-Barr virus B cell stimulation were sequenced by polymerase chain reaction and characterized for VH and VL subgroup. APAF and APAD were also examined by high-resolution electron microscopy for possible ring forms indicative of antiidiotypic V-region interactions. APAF from normal subjects, representing 0.08-0.18% of serum IgG, showed striking relative concentrations of both anti-F(ab')2 and anti-DNA, as well as anti-Sm and anti-Sm/RNP ELISA reactivity. Both APAF and APAD reacting with F(ab')2 or dsDNA on the ELISA plate could be cross-inhibited by F(ab')2 or DNA in solution. Anti-DNA reactivity in normal APAF and APAD was much more sensitive to S1 nuclease treatment than similar fractions from SLE patients. Neither APAF nor APAD from controls produced positive antinuclear immunofluorescence or positive Crithidia staining, whereas these were strongly positive using SLE APAF and APAD. Absorbed rabbit antisera against normal or SLE APAF and APAD showed strong ELISA reactivity against both APAF and APAD, but no residual reactivity with normal Fr II. VL and VH sequencing of monoclonal human IgM antibodies showing both anti-F(ab')2 and anti-DNA reactivity showed relative VH3, V kappa 1 or VH1, V kappa 3 restriction. No evidence of ring forms or V-region "kissing" dimers was obtained when normal or SLE APAD or APAF was examined by high-resolution electron microscopy. IgG anti-F(ab')2 in both normal subjects and SLE patients represents a polyreactive Ig subfraction with concomitant anti-DNA, anti-Sm, and anti-Sm/RNP specificities. Anti-DNA reactivity in SLE is qualitatively different from that in normal APAD and APAF since normal APAD and APAF anti-DNA is much more sensitive to S1 nuclease digestion of denatured dsDNA. APAF and APAD share distinct V-region antigens which may be related to prominent VH3 or VH1 antigenic components. No evidence for in vivo complexing of anti-DNA and anti-F(ab')2 as ring forms or antiidiotype-IgG complexes was observed during ultrastructural studies. In both normal individuals and SLE patients, APAF may represent a small polyreactive IgG subfraction which also contains antinuclear and anti-DNA specificities.

Shared V-Region Antigens and Cross-Reacting Specificities of Human IgG Anti-F(ab′)2and Anti-DNA Antibodies

Affinity-isolated IgG anti-F(ab′)2(APAF) and anti-DNA (APAD) from normal subjects as well as patients with systemic lupus erythematosus (SLE) were studied for overlapping antibody specificities as well as shared V-region antigens using rabbit antisera prepared against F(ab′)2fragments of SLE IgG APAD or IgG APAF from normal individuals. When absorbed free of antibody reacting with normal human IgG, both types of rabbit anti-Ids showed cross-reacting antigenic determinants shared by APAF and APAD from both normals and SLE patients. Immunodepletion of APAD or APAF IgG fractions using immunoabsorbents composed of such rabbit anti-SLE F(ab′)2APAD or anti-normal IgG APAF antibodies produced substantial decrements (40–90%) in ELISA anti-F(ab′)2, anti-Sm, anti-Sm/RNP, and anti-DNA reactivity. Parallel decrements in human anti-DNA Id markers F4 and 3I were also recorded after immunoadsorbent depletions of SLE APADs. Absorption of rabbit IgG anti-SLE APAD F(ab′)2antibody with DNA–Sepharose produced a relative increment in ELISA anti-DNA reactivity but a marked parallel decrement in reactivity for the original SLE APAD immunogen. Eluates from DNA–Sepharose contained rabbit epibody showing moderate anti-DNA affinity and high-affinity anti-APAD idiotypic activity. This epibody fraction showed relative concentration of rabbit IgG antibodies capable of blocking combining sites of SLE IgG APAD reacting with DNA on the ELISA plate. Our findings indicate a previously unexpected close antigenic and specificity overlap between human IgG anti-F(ab′)2and anti-DNA antibodies. Moreover, they emphasize a surprising relative infrequency of anti-DNA idiotypic antibodies capable of blocking combining sites in animals immunized with SLE F(ab′)2APAD. This finding may relate to an intrinsic defect of anti-Id regulation in SLE.

Immunologic markers for differentiation of autoimmune responses.

Several approaches have been directed at identifying accurate parameters for the measurement of disease activity in autoimmune disorders, both in humans and in experimental animal models. A great deal of previous effort has focused on determining what constitutes antigenic epitopes on various autologous proteins or tissue components, which then can generate an immune response in the host. Much of this work has been clouded by the fact that normal subjects (both animal and human) seem to mount an immune response to myriad autologous proteins, characterized by the formation of antibodies known as natural autoantibodies. During the course of certain autoimmune diseases such as systemic lupus erythematosus (SLE) or Wegener's granulomatosis (WG), patients produce what appear to be autoantibodies reacting with autologous components such as DNA and Sm antigen (SLE) or proteinase-3 (WG). Low levels of these same autoantibodies are present in IgG derived from normal subjects. Recently, we have found that IgG anti-F(ab')2 from normal subjects, affinity-purified from immunoabsorbent columns of human F(ab_)2 Sepharose, exhibits not only anti-F(ab')2 but also anti-dsDNA and anti-Sm activity. These antibodies constitute an average of 0.02% of normal serum IgG. Similar findings have also been observed in SLE patients with active disease. Our findings suggest that perturbation of the idiotypic network may represent an important fundamental aspect of many autoimmune disorders.

IgG Anti-F(ab′) 2 Antibodies from SLE Patients React with Immunodominant Residues in κ CDRs, but Show Reduced Cκ Region Reactivity

We studied reactivity of affinity-purified human IgG anti-F(ab′) 2 antibodies for antigenic determinants on κ light chains. Variable (VL) and constant (CL) regions of a human κI light chain (EU) were studied for enzyme-linked immunosorbent assay reactivity with monoclonal anti-κ antibodies and human IgG anti-F(ab′) 2 using overlapping heptamers of primary sequence synthesized as peptides on polypropylene pins. Polyclonal IgG anti-F(ab′) 2 antibodies isolated by affinity chromatography from the serum of patients with systemic lupus erythematosus (SLE) were found to react primarily with CDR1- and CDR3-related peptides. The most reactive residues included IL29, TRY32, LEU33, ALA34, GLU90, TYR91, and ASN 92. No striking difference in overall V-region anti-F(ab)2 reactivity profiles was noted when 10 IgG anti-F(ab′) 2 preparations from normal subjects and SLE patients were compared. In contrast, however, when tested against overlapping Cκ heptamer sequences, the reactivity in SLE-associated anti-F(ab′) 2 antibodies was markedly decreased. We report that this difference may reflect a defect in anti-idiotypic control mechanisms in SLE.

Molecular localization of human IgG anti-F(ab′)2 reactivity with variable- and constant-region λ light-chain epitopes

Human IgG antibodies reacting with antigenic determinants on F(ab')2 fragments represent generic antiidiotypic antibodies present in the serum of normal individuals. Additionally, the titers of these antibodies in the sera of patients with systemic lupus erythematosus (SLE) are inversely related to disease activity. Because these autoantibodies recognize predominantly light chain-related epitopes, especially lambda type, we synthesized constant (C)lambda- and variable (V)lambda-related overlapping 7-mer peptides on polypropylene pins to determine anti-F(ab')2-reactive epitopes on human lambda light chains. ELISA reactivity of affinity-purified anti-F(ab')2 antibodies obtained from normal individuals and from patients with SLE, as well as murine anti-human light-chain monoclonal antibodies specific for C lambda and V lambda subgroup-related determinants, was tested using the overlapping 7-mers of human lambda light-chain sequence. The patterns of reactivity against C lambda-related peptides were similar in both normal and SLE-derived anti-F(ab')2 antibodies. However, reactivity profiles against V lambda-related peptides were distinctively different between the normal and the SLE-associated anti-F(ab')2 autoantibodies. A decrease in reactivity among the SLE IgG anti-F(ab')2 antibodies was noted for particular amino acid V lambda complementarity-determining region (CDR) residues, including glycine at positions 27 and 54, alanine at 16 and 37, and tyrosine at 28 and 91. This different pattern of reactivity from normal may indicate that in SLE there is a failure of antiidiotypic control mechanisms, as reflected by a defect in production of antibody to immunodominant V lambda CDR residues.

Striking inverse correlation between IgG anti-F(ab′)2 and autoantibody production in patients with cold agglutination

Striking inverse correlation between IgG anti-F(ab′)2 and autoantibody production in patients with cold agglutination

Influence of anti-IgG antibodies on graft outcome in live related donor renal transplantation

To study the role of pretransplant IgG anti-F(ab)2γ and IgG anti-Fc antibodies on the outcome of live related donor (LRD) kidney transplantation, serum samples from 60 recipients and 20 normal controls (NC) were tested using enzyme immunoassay. Patients with well-functioning grafts (WFG) after 1 year of follow-up had significantly higher IgG anti-F(ab)2γ activity expressed as mean optical density measured at 405 nm, i.e. 0.426 ± 0.06 as compared to NC (0.167 ± 0.046) or patients undergoing reversible rejection (RR) (0.145 ± 0.043) and irreversible rejections (IR) (0.26 ± 0.01). However, patients with IR had higher IgG anti-Fc activity (0.424 ± 0.2) than the WFG group (0.1 ± 0.02) and NC (0.095 ± 0.02), with the RR group values in between (0.248 ± 0.06). The same trend was observed when the data were analysed according to the serum creatinine levels. We conclude that in the LRD renal transplant situation, pretransplant serum IgG anti-F(ab)2γ activity has a protective effect on graft survival while IgG anti-Fc has a detrimental effect on graft outcome.

The natural human IgG anti-F(ab')2 antibody recognizes a conformational IgG1 hinge epitope.

Natural IgG anti-F(ab')2 Abs are part of the physiologic immune repertoire and have important immunoregulatory functions. Although previous work suggested that some of these Abs recognize epitopes located in the constant region of the F(ab')2 molecule, an exact epitope mapping has not been performed. We found that the anti-F(ab')2 Ab binds strongly to F(ab')2 but only weakly to Fab fragments. Fab fragments are lacking the core and lower hinge region. In our experiments, we show that the IgG anti-F(ab')2 Ab binds strongly to a synthetic double chain peptide (225-237/225'-237') comprising the core and lower hinge region of the human IgG1 molecule. In contrast, it binds only weakly to the same peptide in monomeric form (225-237) or to a short double chain hinge peptide (225-232/225'-232'). The double chain peptides comprise a cyclic region between the two cystine bridges and an exocyclic region. Previous nuclear magnetic resonance analyses showed that the cyclic portion of the short double chain hinge peptide adopts the same conformation as that found in the intact IgG1 molecule. The dichroic properties of the short and long double chain hinge peptides indicate that they have identical conformations in their cyclic regions, but have different conformations in their exocyclic regions. The conformational differences in the exocyclic regions explain the binding of the Ab to the long double chain hinge peptide and the lack of binding to the short one. The circular dichroism spectrum of the monomeric hinge peptide, which is not recognized by the Ab, is consistent with the absence of an ordered peptide structure. These findings lead us to conclude that the IgG anti-F(ab')2 Ab recognizes a conformational IgG1 hinge epitope.

Striking inverse correlation between IgG anti-F(ab')2 and autoantibody production in patients with cold agglutination

Previous experiments showed that the physiologic IgG anti-F(ab')2 antibody suppresses the response of human autoreactive B cells. In the present study, we analyzed the IgG anti-F(ab')2 antibody in 293 patients with cold agglutination (CA). Their average IgG anti-F(ab')2 titer was not much different (211 +/- 8.3) from that of 279 healthy persons (195 +/- 6.7). However, CA patients with high anti-F(ab')2 titers had low CA autoantibody titers and vice versa (P = .0028; rho = -0.175). The stratification of patients according to the auto-antibody's specificity (anti-I, anti-i, anti-Pr) showed an inverse correlation between anti-F(ab')2 and CA in the anti-I group (P = .0057; rho = -0.180). Interestingly, the association was present only in patients whose disease was caused by noninfectious agents (P < .0001; rho = -0.423). The inverse correlation argues for an important role of the IgG anti-F(ab')2 in the regulation of autoantibody production in CA patients.

Striking Inverse Correlation Between IgG Anti-F(ab')2 and Autoantibody Production in Patients With Cold Agglutination

Abstract Previous experiments showed that the physiologic IgG anti-F(ab')2 antibody suppresses the response of human autoreactive B cells. In the present study, we analyzed the IgG anti-F(ab')2 antibody in 293 patients with cold agglutination (CA). Their average IgG anti-F(ab')2 titer was not much different (211 +/- 8.3) from that of 279 healthy persons (195 +/- 6.7). However, CA patients with high anti-F(ab')2 titers had low CA autoantibody titers and vice versa (P = .0028; rho = - 0.175). The stratification of patients according to the auto-antibody's specificity (anti-I, anti-i, anti-Pr) showed an inverse correlation between anti-F(ab')2 and CA in the anti-I group (P = .0057; rho = - 0.180). Interestingly, the association was present only in patients whose disease was caused by noninfectious agents (P &lt; .0001; rho = - 0.423). The inverse correlation argues for an important role of the IgG anti-F(ab')2 in the regulation of autoantibody production in CA patients.

Distribution and Antigenic Analysis of Circulating F(ab′) 2-Reactive IgG in Patients with HIV-1 Infection

Serum titers and molecular specificity of anti-F(ab′) 2 antibodies were investigated in human immunodeficiency virus type 1 (HIV-1) infection with respect to their supposed cytopenic role on CD4 + cells. The levels of antibodies to F(ab′) 2 fragment and to HIV-1 glycoprotein epitopes were measured by immunoenzymatic methods in an HIV-1 + population, including 86 drug addicts, 12 sexually infected patients, and 1 hemophiliac, grouped into Walter Reed (WR) clinical stages 2 to 6 of HIV-1 infection. Monoclonal F(ab′) 2-reactive IgM and IgG from cloned Epstein-Barr B cell transformants of selected patients were also investigated in regards to their HIV-1 glycoprotein specificities and cytotoxicity to the CD4 + cell membrane antigens (CEM) lymphoblasts by a Terasaki assay. Group A (51 sera from WR2 patients) showed the highest titers of IgG anti-F(ab′) 2 with no correlation to positivities to gp120, whereas sera with undetectable anti-F(ab′) 2 levels from group B (37 WR5 and WR6 patients) and from group C (11 WR3-WR6 patients with lymphocytotoxin-associated lymphopenia) were reactive to the virus envelope. Both anti-F(ab′) 2 monoclonal IgM and IgG failed to cross-react with the HIV-1 glycoproteins and the CD4 + CEM. Based on our data, anti-F(ab′) 2 antibodies are apparently unrelated to the CD4 + lymphopenia occurring in HIV-1-infection. In addition, their inability to bind the HIV-1 gp120 as sequence homologue of the CH1 domain of IgG suggests that their molecular target could include a few epitopes located within the VH and VL regions, thus supporting their potential role of antiidiotype molecules as described in autoimmunity.

Anti-F(ab')2 antibodies in thrombocytopenic patients at risk for acquired immunodeficiency syndrome.

22 homosexual or narcotic addict patients at risk for acquired immunodeficiency syndrome (AIDS) or with AIDS, were studied for the presence of antiimmunoglobulin antibodies and circulating immune complexes (20 were thrombocytopenic, 6 had AIDS). Circulating immune complex levels were 10-fold higher than levels in normal subjects. IgG anti-F(ab')2 antibodies were noted in homosexual as well as narcotic addict patients. Of 16 homosexual patients, 7 had IgG anti-F(ab')2 antibody of moderate to marked titer with broad reactivity against autologous, homologous, and control F(ab')2 fragments. Three others demonstrated limited reactivity against one or two F(ab')2 fragments. The remaining six patients were negative. Six of six narcotic addict patients had IgG anti-F(ab')2 antibody, five with limited reactivity, one with broad reactivity. In contrast, neither elevated circulating immune complexes nor anti-F(ab')2 antibodies were detectable in six autoimmune thrombocytopenic patients. Anti-F(ab')2 antibody could be affinity purified from serum or circulating immune complexes. Anti-F(ab')2 reactivity correlated with circulating immune complex levels, r = 0.83, P less than 0.01.

The specificity of antibodies to the F(ab')2 fragment of human IgG.

The specificity of IgG anti-F(ab')2 antibodies was examined by unfractionated sera of patients with rheumatoid arthritis and also with affinity-purified antibody preparations. Examination of the sera by an enzyme-linked immunosorbent assay, using pooled human F(ab')2 fragments absorbed to microtiter plates, revealed that IgG anti-F(ab')2 antibodies cross-react with human and rabbit IgG and rabbit F(ab')2. IgG anti-F(ab')2 antibodies were purified by affinity chromatography and, when tested by a fluid-phase inhibition enzyme-linked immunosorbent assay, were found to be of 2 types. One fraction, similar to pepsin agglutinator, reacted with human F(ab')2 fragment alone. The other fraction was cross-reactive with human IgG and yet failed to react with idiotopes on Fab or epitopes on Fc fragments. The IgG anti-F(ab')2 antibodies we purified had no reactivity toward a human immune complex prepared from tetanus toxoid and antitoxoid.