Two rapid and simple enzyme immunoassays for human antibodies to Entamoeba histolytica.

Two rapid and simple enzyme immunoassays (EIA) for antibodies to E. histolytica the protozoa causing ambiasis, are described. In the rapid dot EIA, a qualitative procedure, antigens were dried as a small dot (3 mm in diameter) on a thin white opaque polystyrene strip and serum samples were assayed undiluted. The assay required 3 incubation periods, 1 to 3 minutes each, and was completed in 9 minutes, with a positive reaction revealed as a blue color (precipitate) on the antigen dot and negative as colorless. The developed color is stable for permanent record. In the Microwell EIA, a quantitative procedure, antigens were dried in the Microwells. The assay also consisted 3 incubation periods of 15 minutes each, and was completed in 50 minutes. The results in absorbance values were normalized to EIA units (EU). Both tests had good reproducibility, sensitivity and specificity; and highly correlated with 3 other serologic tests. Their reagents can be stored for more than a year. Both tests could be suitable for small and physicians' office laboratories, especially in developing countries.

Antibody levels for cytomegalovirus, herpes simplex virus, and rubella in patients with acquired immune deficiency syndrome.

Significantly higher proportions of patients with acquired immune deficiency syndrome (AIDS) or lymphadenopathy syndrome (LAS) were positive for antibodies to cytomegalovirus (CMV) and herpes simplex virus (HSV) compared with control groups of commercial blood donors. In contrast, no differences were found in the incidence of individuals positive for antibodies to rubella in these groups of subjects. Of those positive for antibodies to CMV and HSV in each group, the mean antibody levels were significantly higher in AIDS-LAS patients compared with the controls. The entire distribution of antibody concentrations to CMV and HSV in AIDS patients was shifted upward, so that significantly more patients showed high values and significantly fewer showed low values, indicating hyperactive humoral immune responses to these viruses. In sharp contrast, the AIDS patients with antibody levels for rubella showed the same distribution of antibody levels as did two groups of controls. No correlation was found between concentrations of CMV and HSV antibodies in individual AIDS-LAS patients.

Rubella antibodies detected by several commercial immunoassays in hemagglutination inhibition-negative sera.

Although a very good correlation was found between the level of rubella antibodies measured by a standard hemagglutination inhibition (HI) test and by an enzyme-linked immunosorbent assay (ELISA) procedure (Cordia R), an appreciable proportion (31%) of ELISA-positive specimens were encountered among HI-negative sera. The reverse was rarely seen. Many of the HI-negative, ELISA-positive sera were also found to be positive for rubella antibodies by one or more other assay methods, including an immunofluorescence assay (IFA) procedure (FIAX), passive hemagglutination (PHA) (Rubacell and PHAST), latex agglutination (Rubascan), and a second ELISA procedure (Rubelisa). The specificity of all of the ELISA-positive HI-negative specimens was substantiated by absorption experiments. In these tests, the ELISA reactivities were blocked by rubella antigens, but not by a variety of tissue culture control antigens or by influenza virus grown on the same cell line. The findings indicate that many of the newer methods available for rubella antibody detection are more sensitive than HI for detecting low levels of rubella antibodies. Until more clinical information is available concerning the protective nature of these low levels of antibody, caution should be exercised in assessing the significance of these results.

Normalized enzyme-linked immunosorbent assay for determining immunoglobulin G antibodies to cytomegalovirus.

A normalized enzyme-linked immunosorbent assay for the determination of immunoglobulin G antibodies to cytomegalovirus is described. The rapid assay involves three 30-min incubations and permits the quantitation of antibody levels with a single-specimen dilution in conjunction with a reference antibody preparation. The results obtained with the normalized enzyme-linked immunosorbent assay correlated closely with the results of complement fixation titrations and another commercially available enzyme-linked immunosorbent assay. The specificity of the procedure was further demonstrated by viral absorption, using cytomegalovirus from two different sources and other viral antigen preparations, including rubella and influenza. The reproducibility of the normalized test results is good and allows for greater uniformity of reporting on a day-to-day basis, as well as between laboratories.