IN VITRO STUDY ON THE IMMUNITY OF CHICKENS AGAINST VIRUSES

Abstract

Immunity, one of the intrinsic defence mechanisms of a living animal, plays an important role in safe-guarding, the animal from many disease infections. Generally, immunity is constituted of two major types of immune responses: (i) The immediate (humoral) hypersensitivity: cells involved could synthesize and release antibodies into the blood circulation either independently or through the interaction with other cells and, (ii) The delayed (cellular) hypersensitivity: the production of a population of immnunologically-active 'sensitized' lymphoid cells. These lymphoid cells are known to play a dominant role in tissue-damaging immune reactions such as in transplantation and tumor rejection. In addition, cell-mediated hypersensitivity is also known to be responsible for many allergic immune reactions to bacteria, fungi, soluble protein and simple chemicals ( Rose and Migram, 1969., Roitt, 1971 ). In man, guinea pig and mice, the important role of cell-mediated immunity against virus infection was well demonstrated (Blanden, 1974). But little works have been done in chickens, particularly towards Newcastle disease virus infection. In chickens, it was demonstrated by Kono and his co-workers (1969) that protection against Newcastle disease virus infection requires an active immunization with virus vaccines. They also claimed that the serum antibody titer was generally intimately correlated with the degree of their resistance. On the contrary, Winterfield and his co-workers (1957) who claimed that the circulating antibody titer of virus-immunized chickens is not always closely related to their degree of resistance when they were challenged with a virulent virus strain. This is further supported by the work of Ileri et. al. (1970) who reported that chickens immunized with Newcastle disease virus (NDV) although their sera were shown to contain very low antibody titer still can show remarkable resistance to the challenged inoculations. Until now, little works have been done to clarify these non-correlating results of the circulating antibody titer and the degree of resistance in chickens against virus infection, particularly during the infection of Newcastle disease virus. Therefore, it is of interest to find out the animal immune mechanisms that occur in chickens during the infection of the NDV. The aim of the present work is to investigate the role of the cell-mediated immune responses in chickens during the infection of Newcastle disease virus.