Analysis of the optimal conditions for the adsorption of type III pneumococcal polysaccharide to plastic for use in solid-phase ELISA

Development and validation of carbodiimide-activated ELISA plate for quantifying IgG levels against Streptococcus pneumoniae capsular polysaccharides

Background: Conventional microtiter plates lack the surface strength needed for effective binding of pneumococcal polysaccharide antigens. This study tackles the limitation by altering the surface of polystyrene plates through carbodiimide activation under acidic pH conditions.Method: The microtiter plates were activated with carbodiimide coupling agents, N,N'-Dicyclohexylcarbodiimide (DCC) and N-Hydroxysuccinimide (NHS). They were subsequently coated with 13 pneumococcal antigens at a concentration of 5 μg/ml with a pH of 3.5. The IgG antibody titer was assessed utilizing the World Health Organization (WHO) ELISA protocol for 30 human serum samples. In addition, validation experiments were conducted to evaluate specificity and precision.Results: The modified plates exhibited two-times higher antibody titers compared to conventional plates across all 13 serotypes. Observations revealed elevated antibody levels, with geometric concentrations ranging between 0.96 μg/ml and 4.24 μg/ml.Conclusion: Carbodiimide activation and acidic pH modification of microtiter plates enhance sensitivity and specificity in detecting pneumococcal antibodies, critical for vaccination planning and immunity assessment.

Serum antibody response to polysaccharides in children with recurrent respiratory tract infections

We evaluated children (15-months old and older) with recurrent upper respiratory tract infections and normal levels of immunoglobulins in serum for specific polysaccharide immunodeficiency using an enzyme-linked immunosorbent assay method. Results showed that of 12 patients vaccinated with Act-HIB vaccine, one did not develop specific antibodies to Haemophilus influenzae type b, demonstrating that such immunodeficiency is present in Costa Rican children.

Immunoglobulin G response of periodontitis patients to Porphyromonas gingivalis capsular carbohydrate and lipopolysaccharide antigens

Porphyromonas gingivalis clonal types that participate in periodontal infections express serologically distinct surface antigens. This investigation sought to determine whether serum antibodies titers against the serotype-specific capsular carbohydrate K antigen and lipopolysaccharide antigens of P. gingivalis might reveal which serotypes are most likely to be responsible for subgingival infections in subjects with adult periodontitis. Immunoglobulin G (IgG) titers to purified K antigen and lipopolysaccharide from different P. gingivalis strains were measured by ELISA for 28 healthy controls and 51 patients with periodontal pockets known to be infected with genetically and serologically distinct P. gingivalis clonal types. Titers to purified K antigen from strains W50, HG184, A7A1-28, 49417, HG1690 and HG1691, representing serotypes K1-K6, respectively, and lipopolysaccharide from strains 381, HG1691 and W50, representing serotypes O1-O3, respectively, were measured for all subjects. Chi-square likelihood ratios, Mann-Whitney tests and receiver-operating characteristic sensitivity-specificity plots were used to compare the accuracy with which titer results for different target antigens classified subjects with or without disease. Results from assays targeting K2, K3, K4, K5, O1 and O2 generally gave poor diagnostic accuracy, whether evaluated separately or as summed titer pairs corresponding to the K/O combinations actually expressed by the target antigen parent strains. Exceptions were O3 (from W50) and K5+O2 (both from HG1690), which gave moderate accuracy in classifying subjects. In contrast, highly significant diagnostic accuracy was achieved using individual K1 (W50) and K6 (HG1691) titer data and K1+O3 (W50) and K6+O2 (HG1691) titer sum values. These observations suggest that P. gingivalis clonal types expressing K/O serotypes matching those of W50 (K1/O3) and HG1691 (K6/O2) are more likely than others to participate in periodontal infections in adult periodontitis patients and thus are more likely than others to express relevant virulence factors.

Simple determination of polysaccharide specific antibodies by means of chemically modified ELISA plates

A new ELISA technique using Nunc CovaLink NH microtiter plates has been developed to measure anticapsular polysaccharide specific antibodies. Capsular polysaccharide (PS) of Haemophilus influenzae type b (PRP) and pneumococcal antigens types 3, 6, 8, 14, 19, 23 were immobilized on CovaLink NH. These are modified plates with secondary amino groups bound to their surface which, in the presence of a water-soluble carbodiimide as coupling reagent, facilitate the direct binding of polysaccharides. We compared the binding characteristics of PS antigens to CovaLink NH and a conventional polystyrene ELISA plate. Checkerboard titration of PS antigens between 0.04-30 micrograms/ml clearly demonstrated that with Covalink NH optimal binding of a pooled serum from immunized donors was achieved for all PS antigens tested at a concentration of 1 microgram/ml, while binding of PS to the conventional plate was rather poor even at concentrations of 30 micrograms/ml. The CVs for the ELISA ranged from 1.1 to 2.8% for intra-assay comparisons and from 3.6 to 7.3% for inter-assay comparisons. In addition, when PRP-IgG antibodies were determined with the CovaLink NH ELISA and compared with the Farr assay an acceptable correlation ( r = 0.89, p < 0.0001) was obtained. The technique described provides a simple and sensitive tool for evaluating specific immunity to PS antigens.

Serum antibody responses to vaccination with 23-valent pneumococcal vaccine in splenectomized patients

Sixty-three patients that have been splenectomized for various disorders were vaccinated with Pneumovax 23, the currently available pneumococcal vaccine. Before and one month after splenectomy, IgG antibodies against 8 pneumococcal polysaccharide antigens (types 3, 4, 6B, 7F, 10A, 14, 19F, and 20) were determined by a highly reproducible and type-specific enzyme-linked immunosorbent assay (ELISA). In order to increase the specificity of the assay, this method involved the use of a capture antibody (F(ab')2-fragments of a type-specific rabbit antipneumococcal hyperimmune serum) to bind the pneumococcal antigens to the plastic surface of microtiter plates and the absorption of these sera with the cross-reacting C polysaccharide. Rates of patients showing a two-fold antibody increase were dependent on pneumococcal type, ranging from 12.7% to 33.3%. Antibody responses of single patients were not uniform for all pneumococcal serotypes investigated. Only one patient responded to all of the eight antigens tested. In spite of relatively low response rates, splenectomized patients should be routinely vaccinated with the pneumococcal vaccine, especially when the low rate of adverse reactions is taken into consideration. It is emphasised that the results of the present study and those reported in the literature have to be compared and interpreted with caution, because the available data on the antibody response to pneumococcal vaccination are based on assays that differ substantially in methodology.

ELISAs for parasitologists: or lies, damned lies and ELISAs

The introduction in 1971, by Engvoll and Perlmann, of enzyme labels in immunoassays represented a significant technical advance. Their enzyme-linked immunosorbent assay (ELISA) proved to be as sensitive as radioimmunoossoys but safer to use. Since then, ELISAs have been widely used in the assay o f anti-bodies and antigens. In this article, Pradhib Venkateson and Derek Wokelin focus on some o f the problems associated with ELISAs when applied to parasitic infections, which can modify antibody responses, by immunosuppression or polyclonal activation. The article also considers optimization, which is an essential step in the establishment o f on ELISA.

Selective biotinylation of Neisseria meningitidis group B capsular polysaccharide and application in an improved ELISA for the detection of specific antibodies

A method is described for the selective biotinylation of meningococcal capsular polysaccharide from Neisseria meningitidis group B and its application to an enzyme-linked immunoabsorbent assay (ELISA) to detect specific antibodies by immobilization on streptavidin-coated microtiter wells. Capsular polysaccharide from Neisseria meningitidis B has been biotinylated by specific periodate oxidation of terminal residues and condensation of the resulting aldehydes with biotin hydrazide, using a spin-column technique in the intermediate purification steps. The ELISA was optimized employing an extended reaction time between the label alkaline phosphatase and its most common substrate, p-nitrophenyl phosphate, together with evaluation of blocking agents to minimize non-specific binding. Specificity was demonstrated by a direct competitive enzyme immunoassay (EIA).