Staphylococcal enterotoxin C: solid-phase radioimmunoassay.

A solid-phase radioimmunoassay test employing 125I-labeled enterotoxin C and polystyrene tubes coated with specific antibody was used for the detection and quantitation of entertoxin C in condensed milk, cheddar cheese, custard, and ham salad. The assay was sensitive to 1 to 10 ng of toxin per g of food; nonspecific inhibitions were 16% or less.

Inhibitory effect of synthetic polyribonucleotides on the primary in vitro immune response.

The synthetic double-stranded polyribonucleotides, poly (rA):poly (rU) and poly (rI):poly (rC), were shown to be potent inhibitors of the in vitro plaque-forming cell (PFC) response to a thymus-dependent (SRBC) and thymus-independent (E. coli 0127 LPS) antigen in mouse C57BL/6 spleen cell cultures. The same polynucleotides had no effect on the PFC response of nude (athymic) mouse spleen cells to E. coli 0127 LPS, suggesting that functional T lymphocytes are necessary for the inhibitory effect. Enhancement effects were modest and inconsistent in the cultures. Poly (rA) and poly (rU) were ineffective as inhibitors. The data indirectly suggest that the inhibition may be due to the early production of interferon by functional T lymphocytes.

Comparative inhibitory effects of antigen and antibody in the staphylococcal enterotoxin solid-phase radioimmunoassay system.

A solid-phase radioimmunoassay employing 125I-labeled enterotoxins and polystyrene tubes coated with specific antibody has been developed for assaying the relative concentrations of antibodies to staphylococcal enterotoxins A and B. Competitive binding occurs between tube-bound antibody and free antibody for binding sites on 125I-labeled enterotoxin. The sensitivity of the system is affected by the amount of antibody on the walls of the tubes, the concentration of 125I-labeled enterotoxin added to the system, and probably by the relative binding affinities of the bound and unbound antibodies. Antibody, 0.01 to 0.07 mug/ml, inhibited the uptake of 125I-labeled enterotoxin by 20%. Both the antibody and antigen solid-phase radioimmunoassay inhibition systems can be appropriately represented by either of the following two models: Loge (Y/1 - Y) = alpha0 + alpha1 LogeX and LogeY = beta0 + beta1 LogeX, where Y is bound activity, X is antigen or antibody concentration for inhibition, and alpha0, alpha1, beta0, and beta1 are regression coefficients. Estimates from the first model were slightly more precise for the antibody system, whereas the reverse was true for the antigen system.

Staphylococcal enterotoxins A and B: solid-phase radioimmunoassay in food.

An immunoassay employing (125)I labeled enterotoxins A and B and polystyrene tubes coated with specific antibodies was used for detection and quantitation of enterotoxin in food. Ham salad, cheddar cheese, custard, condensed milk, and salami were studied. Enterotoxin was successfully determined in all the foods by simple extraction procedures. The assay was sensitive to 1 to 10 ng of toxin per g of food; nonspecific inhibitions were 15% or less.

Antigenic cross-reactivity of staphylococcal enterotoxins.

The antigenic cross-reactivity of staphylococcal enterotoxins types A, B, and C was assessed using anti-A and anti-B antitoxins in the solid-phase radioimmunoassay test. Heterologous reactions were observed. At the 33% inhibition level, B was 18,000 and 5,400 times more effective as an inhibitor in its homologous system than were the heterologous enterotoxins A and C, respectively. Similarly, in the A system, A enterotoxin was 55,000 and 25,000 times more effective than were B and C toxins, respectively, in inhibiting A-anti-A reactions.

Staphylococcal enterotoxin B: solid-phase radioimmunoassay.

An immunoassay employing (125)I-labeled enterotoxin B and polystyrene tubes coated with specific antibody was used for assaying purified and crude enterotoxin. Antibody was adsorbed to untreated polystyrene tubes. Unlabeled enterotoxin competed with (125)I-labeled enterotoxin for antibody-combining sites. The uptake of (125)I-labeled toxin reflected the concentration of unlabeled toxin present. The test is sensitive to 1 to 5 ng of purified and crude enterotoxin B per ml, and cross-reactions with heterologous enterotoxins did not interfere with the specificity. This test possesses the combination of sensitivity and objectivity absent in current methods for assaying enterotoxin and provides a model for investigating other enterotoxin serotypes.

Mechanism of tuberculostasis in mammalian serum. II. Induction of serum tuberculostasis in guinea pigs.

The growth of tubercle bacilli in serum samples of untreated animals depends upon the availability of ionic iron which serves as a growth factor in supporting bacillary multiplication. The amount of available iron in serum is determined by the ratio between iron-saturated and iron-free transferrin; a low value for the ratio is associated with tuberculostasis (e.g., human serum, 0.4), whereas a high value is associated with the growth-supporting quality (e.g., guinea pig serum, 5.6). The treatment of guinea pigs with lipopolysaccharide of Escherichia coli or tuberculous cell wall material consistently and significantly reduced serum iron levels; a similar but less striking effect was observed in BCG-vaccinated animals. Pronounced differences were observed in the time of appearance and duration of serum hypoferremia; in lipopolysaccharide-treated animals, it appeared in 1 day and lasted for several days, whereas in BCG-vaccinated animals it appeared in about 2 weeks and lasted for much longer time periods. The induced hypoferremia was always associated with the concomitant development of serum tuberculostasis which could be neutralized by the addition of iron. These results indicate, therefore, that the mechanism of induced serum tuberculostasis in lipopolysaccharide- or tuberculous cell wall-treated and BCG-vaccinated guinea pigs is the same as that present in tuberculostatic sera of untreated animals.