Submitted to: Comparative Biochemistry and Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/23/2005
Publication Date: 1/10/2006
Citation: Humphrey, B.D., Stephensen, C.B., Calvert, C.C., Klasing, K.C. 2006. Lysine deficiency and feed restrition independently alter cationic amino acid transporter expression in chickens. Comparative Biochemistry and Physiology. Part A 143:218-227. Interpretive Summary: Grains are a relatively poor source of the amino acid lysine. In this study we examined how two important tissues of the chicken immune system ' the bursa and spleen ' respond to lysine deficiency. The bursa is the source of B lymphocytes that produce antibody and the thymus is the source of T lymphocytes that regulate immune function and kill virus-infected cells. In general the bursa responds well to lysine deficiency by increasing its ability to take up lysine from the blood (relative to the abilities of other tissues, such as muscle) and maintains normal cell numbers. In contrast, the thymus responds poorly, does not augment its ability to compete for lysine and the number of cells in the thymus decreases. This suggests that animals preserve the antibody-preserving arm of the immune system during malnutrition while the regulatory, T lymphocyte arm of the immune response is diminished.
Technical Abstract: The effect of a lysine-deficient diet on cationic amino acid transporter (CAT1-3) mRNA expression was determined in broiler strain chickens. Chicks consumed a lysine-adequate (LA; 1.3% lysine) or lysine-deficient (LD; 0.7% lysine) diet. Pair-fed chicks consumed the LA diet in an amount equal to that consumed by LD chicks during the previous day (PLA). The plasma lysine concentration in LD and PLA chicks was similar (P>0.05), and was lower than that of LA chicks (P<0.05). LD chicks had higher plasma corticosterone than LA or PLA chicks (P<0.05). CAT 1-3 mRNA expression in the liver, pectoralis and bursa of LD chicks were lower than that of LA and PLA chicks (P<0.05), and levels were not detectable in the thymus of LD chicks. High affinity CAT mRNA expression was greatest in the bursa of LA and PLA chicks and in the pectoralis of LD chicks (P<0.05). High affinity CAT mRNA expression in isolated bursacytes was 16-fold higher in LD chicks than that of LA chicks (P<0.001). However, in thymocytes high affinity CAT mRNA expression was 5-fold lower than that of LA chicks (P<0.05). Based on the summed amount of high affinity CAT-1 and CAT-3 mRNA expression and on the reduction in tissue growth caused by a lysine deficiency, the priority of the bursa and liver for lysine was greater than the pectoralis and thymus. Among these tissues, mRNA expression of the high affinity CAT isoforms in chicks fed a lysine adequate diet was highly correlated (r2 = 0.51; P<0.001) to a tissue's growth during a lysine deficiency. In the thymus and bursa of LD chicks, CAT mRNA levels differed between resident lymphocytes and their surrounding tissues. By expressing high affinity CAT isoforms, developing lymphocytes may have a greater ability to obtain lysine than their surrounding tissue during a lysine deficiency.