Dot immunobinding assay in comparison with enzyme-linked immunosorbent assay for the detection of bluetongue virus antibodies in sheep

Intestinal mucins: the binding sites for Salmonella typhimurium

Mucus-bacterial interactions in the gastrointestinal tract and their impact on subsequent enteric infections are poorly delineated. In the present study, we have examined the binding of Salmonella typhimurium to rat intestinal mucus and characterized a mucus protein (Mucus-Rs) which specifically binds to S. typhimurium. Both virulent (1402/84), and avirulent (SF 1835) S. typhimurium were observed to bind to crude mucus, however, the virulent strain showed 6 fold more binding as compared to avirulent strain. Fractionation of crude mucus on sepharose CL-6B resolved it into three major peaks. Maximal bacterial binding was observed with a high mol. wt. glycoprotein corresponding to neutral mucin. SDS-PAGE of purified protein (termed Mucus-Rs) under non reducing conditions showed it to be a homogenous glycoprotein (mol. wt. 250 kDa), while under reducing conditions, three bands corresponding to mol. wt. of 118,75 and 60 kDa were observed. Pretreatment of Mucus-Rs with pronase, trypsin and sodium metaperiodate markedly inhibited bacterial binding. GLC analysis of Mucus-Rs showed it to contain Mannose, Glucose, Galactose, Glucosamine, Galactosamine and Sialic acid as main sugars. Competitive binding in the presence of various sugars and lectins indicated the involvement of mannose in the mucus-bacterial interactions. The Mucus-Rs binding was highly specific for S. typhimurium; no significant binding was seen with E. coli and V. cholerae. Thus, we conclude that S. typhimurium specifically binds to a 250 kDa neutral mucin of intestinal tract. This binding appears to occur via specific adhesin-receptor interactions involving bacterial pili and mannose of neutral mucin.

Bluetongue: laboratory diagnosis

Definitive diagnosis of bluetongue virus (BTV) infection, often subclinical in domestic and wild ruminant relies heavily on laboratory techniques for BTV isolation and demonstration of BTV antigens, viral nucleic acids and antibodies. The virus can be isolated from blood components, mainly the erythrocyte fraction, collected from affected animals during the period of febrile response. Semen collected from male animals at the peak of viremia and tissues from affected animals and fetuses may also be used for BTV isolation. The primary procedure for BTV isolation is inoculation of embryonated chicken eggs with a subpassage onto cell cultures (e.g. BKH-21, Vero cell lines). In addition to the conventional techniques such as fluorescent antibody staining and virus neutralization procedures for sero-grouping and serotyping of BTV isolates, immunohistochemical, immunoenzymatic and immunoelectron microscopic techniques, using monoclonal antibodies (MAb), offer more rapid, specific and sensitive approaches for BTV identification and antigen detection. The progress of molecular biology, especially the development of genetic probes for hybridization analysis and polymerase chain reaction techniques for detection of BTV nucleic acids hold the promise of most efficient diagnostic assays. Among the various serogroup-specific assays for antibody detection, the agar gel immunodiffusion (AGID) and competitive (C) ELISA are the most widely used tests. Because of its limitations (i.e. anticomplementary serum and complexity of the procedure) the complement fixation (CF) test is virtually abandoned and is used in only a few laboratories. Although the AGID test is simple to perform and rapid, it is not highly sensitive or quantitative and has limitations in its specificity. Sera containing antibodies to other group of Orbiviruses (e.g. epizootic hemorrhagic disease) may result in non-specific reaction in the AGID test. Among several ELISAs that have recently been developed, the C.ELISA in which a group-specific MAb to BTV is used, has proved to be the most sensitive and specific assay for detection of antibodies to BTV. Following extensive national and international validation, the C.ELISA is gradually replacing the AGID as a universal test to certify ruminants for trade purposes and to diagnose BT infection in domestic and wild animals. The cell culture-based microtiter serum neutralization (MTSN) is the most commonly used assay for the detection of serotype-specific antibodies to the recognized BTVs in animal sera. The MTSN may be used to type virus isolates and also to monitor animal population for specific serotypes of BTV in epidemiological investigations.

Dipstick enzyme immunoassay for rinderpest antibody in cattle

A dipstick enzyme immunoassay (ELISA) has been standardized for the detection of rinderpest antibodies. One hundred and thirty bovine serum samples were analysed by the dipstick ELISA method and the results compared with the conventional plate ELISA method. The sensitivity was found to be similar in both methods. The dipstick ELISA does not require expensive micro-plates and an ELISA reader, and is recommended for use in field laboratories where the qualitative detection of rinderpest antibodies is required.

Comparison of blocking dot ELISA and competitive ELISA, using a monoclonal antibody for detection of bluetongue virus antibodies in cattle

A blocking (B) dot enzyme-linked immunosorbent assay (ELISA), using a monoclonal antibody (mAb) against a group specific antigen of bluetongue virus (BTV) is described for the detection of BTV antibodies to BTV in cattle sera. Dots of BTV antigens were adsorbed to nitrocellulose (NC) strips and/or NC mounted in the windows of dipsticks. After blocking the remaining sites of the NC paper with milk powder solution and immersion in the test sample, the NC strips and dipsticks were exposed to mAb. Bound mAb was detected with peroxidase conjugated anti-mouse IgG (H and L). In the absence of anti-BTV antibody in the test sample, BTV antigen sites were reactive with mAb as indicated by a brown colored dot in the presence of the enzyme substrate, hydrogen peroxide and diaminobenzidine. In the presence of sufficient anti-BTV antibodies no color reaction was observed. The performance of these assays in detecting anti-BTV antibody in field blood eluate samples, prepared from whole blood dried on filter paper, from 395 bluetongue-free cattle in Canada and 635 sentinel cattle in Florida, USA, was evaluated and compared with the standard competitive (C) ELISA. The specificity of the dipstick B-dot ELISA was identical to that of the C-ELISA in testing of BT-free Canadian cattle but not in the testing of samples from the sentinel cattle in Florida, resulting in values of 100% diagnostic and 88.9% relative specificity, respectively. Based on the C-ELISA, the specificity of the NC strip B-dot ELISA was low and in the same order as that of the dipstick assay.(ABSTRACT TRUNCATED AT 250 WORDS)

Dot immunobinding assay for the detection of bluetongue virus antibodies in sheep experimentally inoculated with bluetongue virus type 1

Dot immunobinding assay (DIA) was evaluated for the detection of bluetongue virus (BTV) antibodies in sheep experimentally inoculated with BTV 1. Serum samples collected on 14, 21, 28, 43 and 60 day post infection (dpi) were positive for precipitating antibodies by the agar gel precipitation test (AGPT) while antibodies could be detected as early as 7 dpi by DIA and ELISA. Virus neutralizing antibodies were detected first at 14 dpi. The sensitivity of the four tests was compared on the same serum samples collected at different intervals. The results indicated that DIA was more sensitive than AGPT and the serum neutralization test and as sensitive as ELISA. Thus due to sensitivity simplicity and economy, DIA could replace AGPT for diagnosis and serological survey for BTV infection in animals.