Research Note: Precipitin in Chicken Sera Reactive against Tryptose Phosphate Broth

Abstract

Agar-gel precipitin (AGP) tests conducted to detect antibody against Marek's disease virus (MDV) in chicken sera sometimes gave a line of precipitation unrelated to MDV. The MDV antigen was prepared by disrupting MDV-infected cultured chick kidney cells suspended in cell culture medium. The reactive antigen was determined to be the tryptose phosphate broth (TPB) (Difco Laboratories, Detroit, Mich.) comprising 10% of the culture medium (Calnek and Adldinger, unpublished data, 1971) (see Fig. 1). Positive serums were from a specific-pathogen-free (SPF) flock of chickens never inoculated with any substance, and were first observed when the birds were 16 weeks old. The number of reactors increased as the flock became older. Positive birds usually continued to react, but with some exceptions. To learn whether such reactors were peculiar to that flock, sera were collected and tested from other SPF departmental flocks and from unisolated flocks on commercial-type farms. AGP tests were performed as described (2) except that the 1% agar was buffered with O.O1M Tris-HCl, pH 7.3, rather than veronal. Antigen, in the center well, was a 1-in-10 dilution of tryptose phosphate broth in Tris-buffered saline (0.14M NaCI, 0.01M Tris-HCl, pH 7.3). Each test serum was placed in a peripheral well adjacent to one containing known positive serum in order to ascertain that the lines of precipitation from various samples were identical. Tests were conducted in a moist chamber held at room temperature. Single lines of precipitation were usually observed at 48 hours, and final readings were made at 72 hours.