The Mannan-binding lectin (MBL) response to viral infection in chickens

Mannan-binding lectin (MBL) is a glycoprotein belonging to the C-type lectin superfamily. MBL is a carbohydrate-binding protein that selectively recognizes a number of structural oligosaccharide components on the surface of microorgamisms in the presence of calcium. When MBL binds to a microorganism, the complex promotes killing of the microorganism either by acting directly as an opsonin or by activating the lectin complement pathway, thereby playing a major role in the first-line innate immune defense against bacteria, viruses and parasites. MBL is found in serum and is synthesized by hepatocytes in the liver. The concentration of MBL increases during an infection and the MBL is therefore a typical acute-phase reactant. To gain insight into the function of MBL, the acute-phase response of MBL was investigated by experimental inoculation with avian infectious bronchitis. virus (EBV) at different times. The acute-phase response on day-3/4 postinfection showed a significant difference depending upon the time of inoculation of the virus isolate. Chickens inoculated at 9 a.m. (light) had a significantly higher concentration of MBL in serum compared to chickens inoculated at 9 p.m. (dark). Furthermore, the specific antibody titer to IBV was measured and found to be inversely proportional to the MBL level. For farther investigation of the function of MBL, we have selected chickens for high or low MBL level in serum. These chickens were analyzed at the DNA level and a found polymorphism seems to reflect the two groups, indicating that the polymorphism is a functional difference.