Dissociation of antiviral and antitumor immunity in resistance to Marek's disease.

Immunization of chickens either with gluteral-dehyde-inactivated chicken kidney cells infected with Marek's disease (MD) virus or with glutaraldehyde-inactivated cells of MD lymphoma-derived continuous lymphoblastoid cell lines protected against MD. The former type of immunity was associated with an immunologic suppression of virus replication and virus antigen production after challenge with virulent virus, but lymphocytes specifically cytotoxic to cells bearing MD tumor antigens were not detected. In the latter type of immunity, virus multiplication was not affected; some evidence of the stimulation of cell-mediated antitumor immunity was found. The results supported the view that immunity to MD may be directed against either virus-specific or tumor-specific antigens and that in natural resistance to MD both mechanisms may be operative.

Estimation of thyroidal radioiodide clearance in the domestic fowl (Gallus domesticus).

A method for estimating thyroidal clearance of radioiodide from the blood plasma of the domestic fowl is described. It differed from published methods in a number of ways. (1) It utilized total thyroid radioiodide concentration (IT) and did not require the use of goitrogens or the separation of free and protein-bound components. (2) Radioiodide was injected intravenously rather than by other routes. (3) Plasma radioiodide concentration (IB) was determined from several serial samples from each bird rather than once only. (4) The method allowed the clearance constant (kappa; microliter/min per mg) to be estimated for individual birds, rather than from groups, thereby enabling effective replication for comparative experiments. The constant was estimated from the model dIT/dt = kappaIB, measurements being made within 120 min after injection to ensure that exit of radioiodide from the thyroid was negligible. The improved method resulted in estimates of clearance constants which agreed well with published findings.

Effects of dietary corticosterone on peripheral blood lymphocyte and granulocyte populations in immature domestic fowl.

Four-week-old chickens were fed on diets containing 0, 5, 10, 20 and 40 mg corticosterone per kg for eight days. Packed cell volume (PCV), the numbers of granulocytes (G) and lymphocytes (L), the G:L ratio and plasma corticosterone concentration were measured. Plasma corticosterone concentration was increased by dietary corticosterone from day 2 onwards. The number of lymphocytes was increased by serial bleeding but dietary corticosterone depressed the response and caused a dose-related lymphocytopenia from day 1. There was a dose related increase in granulocytes from day 4 and a dose-related increase in G:L ratio from day 1. A dose-related increase in PCV was evident only on days 2 and 4. Correlation coefficients showed little evidence of relationships between plasma corticosterone concentrations and the recorded blood variables.

Sampling broiler house litter for coccidial oocysts.

1. A method of sampling the surface litter of commercial broiler houses for laboratory estimation of numbers of coccidial oocysts is described. 2. The resulting estimates can be regarded as indices of the total number of oocysts present in the house at the time of sampling. 3. Using material from a variety of sources it was shown that reliable estimates for many practical purposes can be achieved with few samples, unless the birds are less than 3 weeks old. 4. Oocyst numbers usually reached a peak 4 to 5 weeks after introduction of the birds and then rapidly declined in the next few weeks.

Effects of dietary corticosterone on the growth and metabolism of immature Gallus domesticus.

Four-week-old chicks were fed on diets containing corticosterone (0, 5, 10, 20, and 40 mg/kg) for 9 days. Food intake, weight gain, plasma concentrations of corticosterone and other constituents, some organ weights, and adrenal cholesterol concentration were measured. Plasma corticosterone concentration was increased (P less than 0.05) by dietary corticosterone, particularly at the two highest rates of inclusion. The concentrations of glucose, cholesterol, triglyceride, protein, and uric acid in the plasma increased (P less than 0.05) with increasing concentrations of dietary corticosterone. Growth rate and relative weight of the cloacal bursa declined (P less than 0.05), while the relative weight of the liver increased (P less than 0.01), with increasing dietary corticosterone; relative weights of the spleen and adrenals were not significantly affected, nor was the adrenal concentration of cholesterol. Abdominal fat was increased sixfold by the two highest corticosterone concentrations.

Taxonomic studies on strains of avian infectious bronchitis virus using neutralisation tests in tracheal organ cultures.

The antigenic relationships of 24 strains of avian infectious bronchitis virus (IBV) were investigated by serum neutralisation tests performed in chick embryo tracheal organ cultures. The serum dilution that neutralised 100 median ciliostatic doses (CD50) of virus was estimated from the linear relationship between varying concentrations of each virus strain and the neutralisation titre of homologous antiserum; this dilution defined 1 antibody unit. Antisera diluted to contain 20 antibody units were then tested by neutralisation against 1.5--2.5 log10 CD50 of each strain. Clusters of both strains and antisera in turn were established by methods of numerical taxonomy using as measures of resemblance Euclidean distance and correlation coefficient, and by analysis by principal components. These analyses identified a group of 8 similar strains; neutralisation of the remaining 16 strains was slight. Similar results were obtained by classifying antisera, except that a further group of 3 antisera was demonstrated, each having a neutralising capacity for most strains. Implications for vaccine formulation are discussed.

Transient effect of cyclophosphamide on vaccinal immunity to Marek's disease.

Cyclophosphamide treatment of chicks abrogated the induction of immunity against Marek's disease (MD) by the herpesvirus of turkeys, but immunity eventually developed if a sufficient interval was allowed to elapse between vaccination and challenge. Vaccinated, cyclophosphamide-treated chicks showed severe suppression of antibody and immunoglobulin production even when immunity to MD was present, suggesting that resistance was not mediated by humoral immunity. Bursa and thymus weights of chicks were markedly reduced 7 days after treatment with cyclophosphamide, but at 35 and 70 days the mean weight of the thymus, but not of the bursa, was considerably restored. The results suggest that cyclophosphamide interferes with vaccinal immunity by an effect on the thymus and cell-mediated immunity, and not by an effect on the bursa and humoral immunity.