AvBD10

A novel avian β-defensin (AvBD), AvBD10, was discovered in the liver and bone marrow tissues from Chinese painted quail (Coturnix chinensis) in the present study. The complete nucleotide sequence of quail AvBD10 contains a 207-bp open reading frame that encodes 68 amino acids. The quail AvBD10 was expressed widely in all the tissues from quails except the tongue, crop, breast muscle, and thymus and was highly expressed in the bone marrow. In contrast to the expression pattern of AvBD10 in tissues from quail, the chicken AvBD10 was expressed in all 21 tissues from the layer hens investigated, with a high level of expression in the kidney, lung, liver, bone marrow, and Harderian glands. Recombinant glutathione S-transferase (GST)-tagged AvBD10s of both quail and chicken were produced and purified by expression of the two cDNAs in Escherichia coli, respectively. In addition, peptide according to the respective AvBD10s sequence was synthesized, named synthetic AvBD10s. As expected, both recombinant GST-tagged AvBD10s and synthetic AvBD10s of quail and chicken exhibited similar bactericidal properties against most bacteria, including Gram-positive and Gram-negative forms. However, no significant bactericidal activity was found for quail recombinant GST-tagged AvBD10 against Salmonella choleraesuis or for chicken recombinant GST-tagged AvBD10 against Proteus mirabilis.

Avian coccidiosis is caused by the intracellular protozoan Eimeria, which produces intestinal lesions leading to weight gain depression. Current control methods include vaccination and anticoccidial drugs. An alternative approach involves modulating the immune system. The objective of this study was to profile the expression of host defense peptides such as avian beta-defensins (AvBDs) and liver expressed antimicrobial peptide 2 (LEAP2), which are part of the innate immune system. The mRNA expression of AvBD family members 1, 6, 8, 10, 11, 12, and 13 and LEAP2 was examined in chickens challenged with either E. acervulina, E. maxima, or E. tenella. The duodenum, jejunum, ileum, and ceca were collected 7 d post challenge. In study 1, E. acervulina challenge resulted in down-regulation of AvBD1, AvBD6, AvBD10, AvBD11, AvBD12, and AvBD13 in the duodenum. E. maxima challenge caused down-regulation of AvBD6, AvBD10, and AvBD11 in the duodenum, down-regulation of AvBD10 in the jejunum, but up-regulation of AvBD8 and AvBD13 in the ceca. E. tenella challenge showed no change in AvBD expression in any tissue. In study 2, which involved challenge with only E. maxima, there was down-regulation of AvBD1 in the ileum, AvBD11 in the jejunum and ileum, and LEAP2 in all 3 segments of the small intestine. The expression of LEAP2 was further examined by in situ hybridization in the jejunum of chickens from study 2. LEAP2 mRNA was expressed similarly in the enterocytes lining the villi, but not in the crypts of control and Eimeria challenged chickens. The lengths of the villi in the Eimeria challenged chickens were less than those in the control chickens, which may in part account for the observed down-regulation of LEAP2 mRNA quantified by PCR. Overall, the AvBD response to Eimeria challenge was not consistent; whereas LEAP2 was consistently down-regulated, which suggests that LEAP2 plays an important role in modulating an Eimeria infection.

The aim of this study was to determine the mechanism by which expression of avian β-defensins (AvBD) in the follicular theca tissue was regulated. It was examined whether their expression was stimulated directly by LPS or indirectly through proinflammatory cytokines (IL-1β and IL-6) induced by LPS. Theca tissues of ovarian follicles were collected from White Leghorn hens. The specimens of those theca tissues were cultured in TCM-199 culture medium and stimulated by lipopolysaccharide from Salmonella minnesota (LPS), recombinant chicken IL-1β, or recombinant chicken IL-6. In the first experiment, changes in the expression of IL-1β, IL-6, AvBD10, and AvBD12 in response to LPS stimulation were examined by quantitative reverse-transcription PCR. The AvBD10 and 12 had been known to be expressed in the theca. In the second experiment, changes in the expression of AvBD10 and 12 in response to recombinant chicken IL-1β or IL-6 stimulation were examined by quantitative reverse-transcription PCR. Density of AvBD12 protein after IL-1β stimulation that showed changes in the gene expression was analyzed by Western blotting. In the first experiment, LPS was able to induce IL-1β and IL-6, but not AvBD10 or AvBD12. In the second experiment, IL-1β was able to upregulate significantly the expression of AvBD12 mRNA and protein. However, IL-6 did not exert significant effects on the expression of AvBD10 and AvBD12. It is suggested that LPS may stimulate theca cells to produce proinflammatory cytokines, whereas, in turn, IL-1β stimulates those cells to synthesize AvBD12, which may be able to attack infectious gram-negative bacteria.