New method that uses binding of immunoglobulin A to group A streptococcal immunoglobulin A Fc receptors for demonstration of microbial immunoglobulin A protease activity

Fc receptor--more answers, more questions

Fc receptors, belonging to the most important surface structures of a number of cells participating in the immune processes, have been intensely studied during the past decade. The present review summarizes the contemporary knowledge of the specificity and heterogeneity of Fc receptors and of factors influencing their expression, and includes some views on their function. In addition, it mentions their relationship to other cell surface structures, expression of Fc receptors during ontogeny of the organism and in certain diseases. Finally, data concerning the isolation and biochemical characterization of the Fc receptor molecule are presented.

A rapid method for the detection and quantitation of IgA protease activity by macrobore gel-permeation chromatography

A rapid assay to detect and quantitate immunoglobulin A1 (IgA1) protease activity was developed by the use of a high-performance gel-permeation chromatography column. The assay measured the disappearance of intact substrate and the emergence of cleavage fragments and the results could be expressed in absolute units. The utility of the assay was demonstrated in the partial purification of an IgA1 protease from a strain of Haemophilus influenzae.

A sensitive enzyme-linked immunosorbent assay for IgA protease activity

IgA proteases are enzymes of bacterial origin capable of cleaving human IgA1 into Fab alpha and Fc alpha fragments. This article describes a solid phase assay employing microamounts of protease as well as substrate for the quantitation of IgA protease activity. IgA substrate (IgA paraprotein, colostrum S-IgA, or simply diluted saliva) is bound to the surface of a polystyrene microtitration plate coated with anti-light chain antibody in order to assure binding of substrate molecules through Fab alpha. Incubation of such bound substrate with IgA protease, either prepared or as protease-producing whole bacteria, results in release of Fc alpha whereas Fab alpha is still retained after wash. Loss of Fc alpha is detected through a reduced capacity for binding of peroxidase-conjugated anti-alpha-chain antibody, the binding of which is detected using standard ELISA techniques. Simplicity and extreme sensitivity make this assay useful for quantitation of IgA protease activity, for kinetic studies of the enzyme, and for detection of IgA protease activity in single agar plate colonies of bacteria.

Quantitative screening of clinical isolates for immunoglobulin A protease production

The production of immunoglobulin A (IgA) protease is a potentially useful marker in differentiating pathogenic from nonpathogenic species of clinical isolates; however, current quantitative assay methods are too tedious for routine application. A simple quantitative method was developed to screen clinical isolates for IgA protease production. This method is based on the specificity of reaction between IgA and alpha chain-specific antiserum in an immunochemistry analyzer (Beckman Instruments, Inc., Brea, Calif.). Colonies of IgA protease producers (Streptococcus sanguis, Streptococcus pneumoniae, Neisseria gonorrhoeae, Neisseria meningitidis, and Haemophilus influenzae) were picked from solid media, transferred to brain heart infusion containing IgA1, and incubated at 37 degrees C for at least 2 h to provide a detectable decrease in IgA concentration. The standard deviation for randomly picked colonies within a species was about +/- 15%. Several IgA protease-negative species caused no detectable reduction in the IgA content of the system. The specificity of the IgA measurement eliminates the requirements for extensive purification and radiolabeling of substrate and provides the basis for a well-defined IgA protease activity unit (micrograms of IgA1 cleaved per minute per milliliter of culture).

Nephelometric assay for the immunoglobulin A1-protease produced by the oral bacterium Streptococcus sanguis

Streptococcus sanguis, an initiator of human dental plaque, produces an endopeptidase which cleaves immunoglobulin A1 (IgA1) at the hinge region. A rapid nephelometric assay was developed for the quantitation of IgA1-specific protease activity. The protease was produced in dialysis cultures which yielded cell-free fluids having 14 times the specific activity of conventional cultures. Assay was based on the difference in detectable IgA1 concentrations at the start and termination of the reaction; IgA1 concentrations were determined by rate of complex formation with IgA-specific antibody. The rates of IgA1 cleavage were linear during incubations up to 3 h if enzyme preparations were sufficiently diluted. The assay resolution was less than that achieved with sodium dodecyl sulphate-polyacrylamide gel electrophoresis, but 1 h incubation of protease-IgA1 reaction mixtures was adequate for measurement. The pH optimum for the reaction was 7.0 and the calculated Km was 5.6 X 10(-5)M IgA1. The optimal incubation temperature was in the range of 37-40 degrees C; the enzyme lost all activity at 55 degrees C.