Shared epitopes of avian immunoglobulin light chains.

Like all jawed vertebrates, birds (Aves) also produce antibodies i.e. immunoglobulins (Igs) as a defence mechanism against pathogens. Their Igs are composed of two identical heavy (H) and light (L) chains which are of lambda isotype. The L chain consists of variable (VL), joining (JL) and constant (CL) region. Using enzyme immunoassays (EIA) and two monoclonal antibodies (mAbs) (3C10 and CH31) to chicken L chain, we analysed their cross-reactivity with sera from 33 avian species belonging to nine different orders. Among Galliformes tested, mAbs 3C10 and CH31 reacted with L chains of chicken, turkey, four genera of pheasants, tragopan and peafowl, but not with sera of grey partridge, quail and Japanese quail. Immunoglobulins of guinea-fowl reacted only with mAb 3C10. Both mAbs reacted also with the L chain of Eurasian griffon (order Falconiformes) and domestic sparrow (order Passeriformes). Sera from six other orders of Aves did not react with either of the two mAbs. EIA using mAbs 3C10 and CH31 enabled detection of antibodies to major avian pathogens in sera of chickens, turkeys, pheasants, peafowl, Eurasian griffon and guinea-fowl (only with mAb 3C10). The N-terminal amino acid sequence of pheasant L chain (19 residues) was identical to that of chicken. Sequences of genes encoding the L chain constant regions of pheasants, turkey and partridge were determined and deposited in the public database (GenBank accession numbers: FJ 649651, FJ 649652 and FJ 649653, respectively). Among them, amino acid sequence of pheasants is the most similar to that of chicken (97% similarity), whereas those of turkey and partridge have greater similarity to each other (89%) than to any other avian L chain sequence. The characteristic deletion of two amino acids which is present in the L chain constant region in Galliformes has been most likely introduced to their L chain after their divergence from Anseriformes.

Ornithobacterium rhinotracheale has neuraminidase activity causing desialylation of chicken and turkey serum and tracheal mucus glycoproteins.

Neuraminidases (sialidases) are virulence factors of several poultry pathogens. Ornithobacterium rhinotracheale is a well known poultry pathogen causing respiratory disease in chickens and turkeys all over the world. We investigated whether O. rhinotracheale has neuraminidase enzymatic activity (NEAC). We tested NEAC in 47 O. rhinotracheale strains isolated from turkeys and chickens in eight countries. All strains showed relatively strong NEAC and considerable levels of NEAC were detected also in "cell-free supernatants" of their pelleted cells. Zymography using neuraminidase-specific chromogenic substrate indicated that a protein with molecular mass of ~40kDa and isoelectric point (pI) of ~8.0 is a putative neuraminidase of O. rhinotracheale. Notably, the genome of the type strain of O. rhinotracheale, DSM 15997 contains a gene (Ornrh_1957) encoding a putative neuraminidase with such Mw (39.5 kDa) and pI (8.5). We sequenced a corresponding genomic region of 20 O. rhinotracheale strains and found five distinct types of the neuraminidase gene (termed nanO) sequences. Most diversified nanO sequence was found in two strains isolated from chickens in Hungary in 1995. Their nanO sequences differ from that of the type strain (LMG 9086(T)) in 27 nucleotides. O. rhinotracheale neuraminidase showed capacity to cleave sialic acid from chicken and turkey glycoproteins. It cleaved sialic acid from SAα(2-6)gal moiety of their serum proteins, including immunoglobulin G (IgG) and transferrin. O. rhinotracheale also desialylated chicken and turkey tracheal mucus glycoprotens with SAα(2-3)gal moieties. This study provides the first evidence that O. rhinotracheale has neuraminidase which can desialylate glycoproteins of its natural hosts.

Demonstration of neuraminidase activity in Mycoplasma neurolyticum and of neuraminidase proteins in three canine Mycoplasma species.

Neuraminidases are virulence factors in many pathogenic microorganisms. They are present also in some Mycoplasma species that cause disease in birds, dogs and alligators. Thirty-seven Mycoplasma species have been examined previously for neuraminidase (sialidase) activity, whereas many of the species causing disease in man, ruminants, pigs, rodents and other animals have not. In this study neuraminidase enzymatic activity (NEAC) was examined in 45 previously untested Mycoplasma species, including those causing diseases in man, farm animals and laboratory animals. The only species in which NEAC was found was Mycoplasma neurolyticum, specifically, its type strain (Type A(T)) which is capable of inducing neurologic signs in inoculated young mice and rats. The NEAC of washed cells was relatively weak, but it differed even more than 10-fold among cells of cultures derived from individual colonies of M. neurolyticum. A weak NEAC was also detected in the supernatant of the M. neurolyticum broth culture. Canine Mycoplasma spp. with high sialidase activity reported previously, Mycoplasma canis, Mycoplasma cynos and Mycoplasma molare had 100-fold more NEAC than M. neurolyticum, but apparent differences in NEAC levels existed among strains of M. canis and of M. cynos. Zymograms using neuraminidase-specific chromogenic substrate were used to show proteins having NEAC. In M. canis (a field isolate Larissa and the type strain PG14(T)), M. cynos (isolate 896) and M. molare (type strain H542(T)) proteins with NEAC had molecular masses of ∼130kDa, 105kDa and 110kDa, respectively. Identification of these neuraminidases could provide the basis for their molecular characterization.