Collectins in innate immune defense of pigs and chickens

Abstract

In the Netherlands, the number of chickens and pigs exceeds the number of human inhabitants by far. Therefore, combating infections in livestock is not only of economical importance, but also of great importance to public health. The innate immune system provides a first line defense against infectious pathogens, and its effector mechanisms rely on the recognition of features that are common to many pathogens. These features, known as pathogen-associated molecular patterns can be recognized by pattern recognition molecules at the site of infection, which is often an epithelial surface like the lung, skin or gastro-intestinal tract. Collectins, an important group of pattern recognition molecules, have been reported to be expressed in many epithelial surfaces. In the lung, Surfactant Protein-D (SP-D) contributes to the maintenance of a sterile respiratory system. Its role in the gastro-intestinal tract, which is dominated by the presence of micro-organisms, is less clear. Therefore, we investigated the interaction of porcine SP-D (pSP-D) with various Gram-negative bacteria isolated from the porcine intestine. It was shown that while pSP-D is capable of reducing growth rates of E. coli K12, the growth rates and survival of pathogenic bacterial strains isolated from the porcine intestine remained unaffected. Furthermore, pSP-D was shown to affect bacterial adhesion- and invasion- characteristics, leading to a significant increase in adhesion and invasion of bacteria into IPI-I2 cells. It is not yet clear what the mechanism behind these effects is, but it could reflect a scavenger function for pSP-D in the intestine. In the chicken, only two collectins had been described thus far. In this thesis, we report the discovery of three new chicken collectins, chicken Collectin 1-3 (cCL-1, -2,and -3) and one chicken lectin, chicken Lung Lectin (cLL). Results from this study support the assumption that cCL-1, -2 and -3, together with their respective mammalian homologues CL-L1, CL-K1 and CL-P1 represent three new unique classes within the collectin protein family. Because of its predominant expression in the chicken respiratory tract, the newly discovered chicken lectin was designated chicken Lung Lectin (cLL). To investigate whether these chicken (col)lectins are involved in avian innate immunity, their mRNA expression levels during bacterial and viral infections were investigated. Samples derived from three infection-models were analyzed, and the results showed that mRNA expression of chicken (col)lectins cCL-1, cCL-2, cSP-A and cLL can be affected by both bacterial and viral infections. We also investigated the structural and functional aspects of cLL. To this end, recombinant cLL was successfully produced in HEK-293 EBNA cells. Characterization of recombinant cLL revealed that this protein is capable of binding sugars, and, as predicted from its sequence, does so in a calcium-dependent manner. In addition, cLL showed anti-viral activity against avian IAV in our preliminary tests, and HAA-inhibition of a human isolate of IAV was shown. Further investigation into the function of the (col)lectins can provide insight how they are involved in innate defense against invading pathogens, and exploiting their properties and functions may provide an alternative strategy towards preventing infections in pigs and poultry.