CD8+ T cell-coccidia interactions

Host responses to coccidian parasites involve many facets of the immune system, including antigen-specific as well as antigen-nonspecific components. Hyun Lillehoj and James Trout here review the evidence that cell-mediated responses are probably the main line of defense against coccidial infection.     

Eimeria acervulina: cloning of a cDNA encoding an immunogenic region of several related merozoite surface and rhoptry proteins.

A cDNA encoding a recombinant Eimeria acervulina antigen, designated EAMZp30-47, that contains an epitope shared among several surface and rhoptry proteins of merozoites was characterized. The respective parasite proteins are between 30 and 47 kDa as revealed by immunostaining of nitrocellulose membrane containing extracts of 125I-labeled merozoites. As indicated by immunofluorescence and immunoelectron microscopic staining, the reactive epitope was localized to both the surface membrane and the internal rhoptries of this asexual stage of the parasite. The recombinant beta-galactosidase fusion protein EAMZp30-47 is 130 kDa, thus representing 15 kDa or 30-50% of the respective parasite protein. Purified EAMZp30-47 stimulates T cells from E. acervulina-immune inbred chickens, but is not recognized by immune chicken serum, suggesting that T cell and not B cell epitopes recognized by the host immune system during a natural infection are present on the recombinant protein. Northern and Southern blot hybridization experiments indicated that expression of EAMZp30-47 is restricted to the merozoite stage of the parasite and the gene occurs as a single copy sequence within the genome.     

The gag gene products of human immunodeficiency virus type 1: alignment within the gag open reading frame, identification of posttranslational modifications, and evidence for alternative gag precursors.

Seven human immunodeficiency virus gag polypeptides were identified in the purified virus and in infected CD4+ lymphocytes by peptide mapping and limited amino acid sequencing of immune-purified proteins. Two gag polyproteins of 55,000 (p55) and 41,000 (p41) daltons were rapidly labeled and readily processed into the major internal gag proteins that were aligned within the gag open reading frame (ORF) as NH2-p16 (MA)-p24 (CA)-p9 (NC)-p7-COOH. The myristoylated p16 (matrix, MA) protein was processed from the myristoylated p55 gag precursor protein. The immunoreactivity of the p16 (MA) protein with region-specific gag antisera and the conservation of the N-terminal myristyl group of the p55 precursor protein in p16 (MA) confirmed its position as the N-terminal-most protein. The p9 (nucleocapsid, NC) protein was localized to residue 378 of the gag ORF, next to the C terminus of the p24/p25 (core antigen, CA) protein. The p9 protein had a repeating Cys residue containing motif which is found in the nucleic acid-binding Cys residue-containing proteins of retroviruses. The p24 (CA) protein, which was localized to residue 133 of the gag ORF, was apparently derived by C-terminal processing of an intermediate polypeptide, p25. Both the mature p24 (CA) and p16 (MA) proteins were phosphorylated at Ser residue(s). We also identified two forms of gag p41 species, one resulting from the C-terminal processing of p55 and the other originating either from N-terminal processing of p55 or from de novo synthesis.     

Effect of triiodothyronine on the expression of T cell markers and immune function in thyroidectomized White Leghorn chickens.

Hypothyroid K-strain chickens were produced by neonatal thyroidectomy and treatment with 6-propyl-2-thiouracil. Thyroidectomized birds were given 0, 1.5, 4.5, 15, or 45 micrograms/kg body wt of triiodothyronine (T3) by daily injection. At 5 weeks of age, thymocytes were prepared for flow cytometric analysis of CT-1a, CD3, CD4, and CD8 expression. Sham-operated birds had the smallest proportion of CT-1a+ cells and the brightest CT-1a+ cells. Unsupplemented thyroidectomized birds presented an inverse picture, while T3-treated thyroidectomized birds were intermediate. Fewer and less brightly labeled CD3+, CD4+, and CD8+ cells were associated with sham-operated birds or with higher levels of T3 replacement. Low levels (1.5 microgram/kg body wt) or no T3 treatment produced a greater proportion of positive, highly fluorescent cells. The ratios of CD4+ to CD8+ thymocytes were increased (P less than or equal to 0.05) by T3 supplementation. Functionally, thyroidectomy produced a decrease in mitogen-stimulated proliferation of peripheral blood lymphocytes. This effect was ameliorated by T3 supplementation. Further, thyroidectomy produced an elevation of plasma growth hormone concentrations. These results suggest that thyroid factors and alterations of thymic status significantly affect the generation of specific thymus-derived lymphocyte populations and their functional capabilities, perhaps due to changes in the thymic microenvironment. These alterations may have important consequences for the development of immunocompetence and disease resistance in chickens.     

Biological Activity of Aflatoxin B2a

The toxicity of alfatoxin B(2a) (hydroxydihydro-aflatoxin B(1)) was studied in several biological systems. Aflatoxin B(2a) is the monohydroxylated derivative obtained from addition of water to the double bond of the terminal furan of B(1). Examination of the sensitivity of a group of microorganisms to B(2a) demonstrated that the inhibitory spectrum was similar to aflatoxin B(1). However, the toxicity of B(2a) was markedly lower than B(1), as measured by the initiation of bile duct hyperplasia in ducklings. Binding of aflatoxin to deoxyribonucleic acid (DNA) was determined by measuring the hypochromicity produced by the nucleic acid at 363 nm and the capacity of increasing amounts of DNA to quench the fluorescence of the toxin was also used as a measure of the binding of toxin to nucleic acid. These tests showed that the DNA-binding capacity of B(2a) was lower than B(1).     

Aflatoxin contamination caused by natural fungal infection of preharvest corn

Summary Aflatoxin contamination of developing corn (Zea mays L.) kernels caused by natural infection byAspergillus flavus Link ex Fries was studied in hybrids developed for the U.S. corn belt and for the southern U.S. and grown at diverse locations in 1977. Planting dates were staggered to examine the effect of crop maturity on infection by the toxin-producing fungus. A broad range of toxin values was observed at harvest; some levels exceeded the highest that had been previously recorded in corn. The highest concentration of aflatoxin B₁ detected was 8030 ppb. Levels of toxin differed significantly among planting dates in Florida and Georgia; the second planting date at these locations contained the highest toxin levels. Elevated concentrations of toxin were characteristic of kernel samples from southern locations and southeast Missouri; at these locations samples from hybrids developed for the south had significantly lower levels of toxin than hybrids developed for the corn belt. Ears with heavy insect damage had higher toxin levels than ears with less evidence of insect attack.Mention of firm names or trade products does not imply that they are endorsed or recommended by the U.S. Department of Agriculture over other firms or similar products not mentioned.