Antibodies against DNA-psoralen crosslink recognize unique conformation

The DNA-psoralen crosslink induced precipitating antibodies in rabbits with a titer of 1:102,400 by direct binding ELISA. The antiserum showed considerable binding with Z-DNA and calf thymus DNA brominated under high salt concentration which has been shown to attain Z-/analogous conformation. Inhibition experiments substantiated the results of direct binding assay. However, the affinity purified IgG showed high degree of specificity for the immunogen and did not recognize nDNA, Z-DNA and brominated DNA as inhibitor. Poly(dG.dC).poly(dG.dC)-psoralen photoadduct was found to be inhibitory. These results indicate that the antibodies are probably recognizing the unique conformation at the site of psoralen crosslinking. The DNA-psoralen crosslink showed significant binding with SLE sera known to have high levels of anti-native DNA antibodies. Affinity purified SLE-IgG in a competition assay pointed out the autoantibody recognition of altered conformation of DNA-psoralen crosslink.

Comparison of the generation of albumin-associated cytotoxic activity in supernatants from ethanol-containing cultures of human blood monocyte-derived macrophages and of two human hepatoma cell lines

The rates of oxidation of ethanol to acetate by human blood monocyte-derived macrophages and the two human hepatoma cell lines PLC/PRF/5 and Hep G2 were studied. The average rates obtained were, respectively, 621, 447 and 596 nmol/h/mg cellular protein. Cultures of these three cell types, containing known quantities of cellular protein per flask, were incubated with 0 or 2 mg ethanol/ml for 72 h and the culture supernatants subjected to affinity chromatography on blue sepharose CL-6B. Pure albumin fractions obtained in this way were adjusted to the same optical density and tested for cytotoxicity against A9 cells. The data showed that the albumin fractions obtained from ethanol-containing macrophage cultures were considerably more cytotoxic than those obtained from ethanol-containing cultures of PLC/PRF/5 and Hep G2 cells. It appeared that, for a given quantity of ethanol metabolised, considerably more acetaldehyde was released extracellularly by macrophages than by the two hepatoma cell lines and that this acetaldehyde bound to albumin to form cytotoxic acetaldehyde-albumin complexes. The data raise the possibility that macrophages are an important source of extracellular acetaldehyde and circulating acetaldehyde-albumin complexes in vivo.

Antigen binding diversity of affinity purified autoantibodies against DNA

Naturally occurring autoantibodies against native DNA (nDNA) in SLE sera showed diverse antigen binding characteristics. The antibodies isolated by affinity chromatography using nDNA linked to Sepharose 4B exhibited specificity towards nDNA and showed strong reactivity with DNA-psoralen photoadduct by direct binding assay and competitive ELISA. The anti-DNA antibody belong to both IgG and IgM immunoglobulin classes and their ratio was 5:1. The possible significance of altered conformation of nDNA in the etiology of SLE has been discussed.

Quantitation of IgM antibodies to the M. leprae synthetic disaccharide can predict early bacterial multiplication in leprosy

Quantitative enzyme-linked immunosorbent assays detecting IgM to the soluble Mycobacterium leprae crude sonicate (CD75) and the synthetic disaccharide antigen coupled to bovine serum albumin (ND-BSA) were assessed for their ability to determine early infection in families/household contacts of leprosy patients and employees of a leprosy center working in close contact with leprosy patients. Although IgM to both antigens (CD75 and ND-BSA) correlated with the bacterial index (BI) assessed histologically on skin-biopsy samples, the level of IgM antibodies to ND-BSA was a much more sensitive indicator of low bacterial loads. A 4.4-fold difference in antibody levels was observed between the mean group levels of endemic controls (N = 116) and tuberculoid leprosy patients with a BI of 0 (N = 88), increasing to sevenfold in tuberculoid leprosy patients with a BI of 1 (N = 20). Using a statistical cut off with endemic controls (mean + 2 S.D.), household/family contacts showed 30% seropositivity (N = 180) as compared to staff contacts who showed 17% seropositivity (N = 55). Percent seropositivity in family contacts was not related to the type of leprosy of the index case (lepromatous vs. tuberculoid) or the duration of treatment of the index case. Age of the individual in the family contact group had a significant influence on seropositivity. These results support the hypothesis that, in this community, factors other than the viable bacterial load of the index case, such as genetic susceptibility, may be influencing the high rate of seropositivity in family contacts. IgM ND-BSA antibodies seem to provide a good indicator of low antigenic loads and could prove to be useful in detecting subclinical infection before the onset of disease. Follow-up studies of these seropositive individuals are in progress to understand the relationship between seropositivity and the progress of clinical disease.

Quantitative antibody ELISA for leprosy

Quantitative enzyme-linked immunosorbent assays (ELISAs) were established to measure IgM and IgG antibody levels to soluble Mycobacterium leprae sonicate (CD60) and to the synthetic disaccharide antigen based on the phenolic glycolipid-I antigen of M. leprae coupled to bovine serum albumin in 46 leprosy patients. Separate reference pools for IgM and IgG antibody were established. The reciprocal of the antibody titer was expressed as the number of arbitrary units in the reference pools which was subsequently used as the calibrator for assessment of units in individual test sera. The dose-response relationship for both IgM and IgG was highly specific and reproducible for both isotypes, as indicated by the intra- and inter-assay coefficients of variation. The distribution of antibody levels are in general agreement with the results from previous studies against different M. leprae antigens. The lepromatous group showed 10- to 100-fold higher IgM antibodies to both the soluble sonicate antigen and the disaccharide as compared to the control group. Very low to undetectable levels of IgM antibodies were observed in the tuberculoid group of leprosy patients. IgG antibodies, on the other hand, were not only present but showed considerable overlap with the lepromatous patient group. Optimized ELISAs, such as the one described in this study, would allow one to address issues such as antibody changes with treatment, antigen clearance, and correlation with other immune parameters associated with disease pathogenesis and protection.

T-cell recognition of the 18-kilodalton antigen of Mycobacterium leprae

The 18-kilodalton (kDa) antigen of Mycobacterium leprae was expressed as a fusion protein with a 2-kDa leader peptide and used in proliferation assays with peripheral blood cells. Fifty percent of untreated tuberculoid leprosy patients and 93% of long-term leprosy contacts responded to the recombinant protein in lymphocyte transformation tests. Comparison of the stimulation indices in the two groups showed that the contacts responded more strongly than the tuberculoid leprosy patients. Seventy percent of Mycobacterium bovis BCG-vaccinated European donors responded, although with low stimulation indices. The isolation of 18-kDa antigen-responsive T-cell lines from a BCG-vaccinated British donor confirmed that the 18-kDa antigen contains at least one cross-reactive epitope. These results indicate that the 18-kDa protein is an important antigen in the immune response to leprosy.