The frequent mutation Gly/Asp in CDR1H may determine a cross-reactive idiotope in anti-I cold agglutinins

Variable domains (VH) of all known anti i/I cold agglutinin (CA) heavy chains are codified by the VH4–21 gene. While anti-i CAs are the expression of gene rearrangement without mutations represented by amino acid changes, anti-I CAs present, among others, a frequent somatic mutation of Gly by Asp at position 31. The hydropathy profile calculated for the CDR1H (position 30 to position 35), as well as some adjacent positions of the heavy chain belonging to anti-i and anti-I antibodies, showed the conformational changes accompanying the replacement of Gly by Asp. A MoAb (LP91), which had been obtained in BALB/c mice immunized with a Fabμ fragment from a monoclonal IgMκIIIb anti-I CA (protein KAU), proved capable of inhibiting human adult erythrocyte cryoagglutination by anti-I CAs but not that of fetal erythrocytes by anti-i CAs. Western blot analysis disclosed that such MoAbs recognized a sequential epitope located in the Fd fragment of all anti-I CAs employed in this study. With the purpose of checking whether Asp31 was involved in the epitope recognized by the MoAb, two peptides, D and G, were synthesized which mimicked the CDR1H structure of anti-I and anti-i, respectively; the MoAb only reacted with peptide D by ELISA. Subsequent experimental results indicate that the Gly/Asp mutation could be associated with the diverse specificity presented by these autoantibodies, a change determining a characteristic epitope/idiotope, recognized by LP91 in the CDR1H

Antibodies from patients with psoriasis recognize n-acetylglucosamine terminals in glycoproteins from Pityrosporum ovale

We have previously reported the finding of circulating antibodies recognizing two proteins of 100 and 120 kD (PO100 and PO120) from Pityrosporum ovale in patients with psoriasis. These antibodies were specific, since they were not detected in normal sera nor in other diseases linked to P. ovale such as seborrhoeic dermatitis or pityriasis versicolor. The present study aimed at further characterizing the specificity of these antibodies. Enzyme-labelled lectins were used to determine the carbohydrate composition of PO120 and PO100. BSII, a lectin that recognizes terminal n-acetylglucosamine (GlcNAc), showed the same banding pattern as sera from patients. Reactivity against these proteins was inhibited after mild oxidation of the carbohydrate moieties of the extract. Treatment of the extracts with lyticase altered the immune reactivity against the PO120 band as seen in Western blot assays. PO100 was not detected after lyticase digestion. Digestion with lysozyme did not alter the immune reactivity of the PO100 and PO120 bands, although the protein pattern in SDS–PAGE was modified. To examine the relevance of anti-GlcNAc antibodies in the immune response to P. ovale in psoriasis, we performed a binding inhibition ELISA. Psoriatic sera that were positive in the ELISA against a heat-denatured extract of P. ovale were rendered negative only by pre-incubation with GlcNAc in a concentration-dependent manner. Our results are indicative that the antibody response to PO100 and PO120 in patients with psoriasis is directed towards terminal GlcNAc residues