User:Abdullah-Al-Zabir

INTRODUCTION

Bangladesh is one of the developing countries of the world. Most of the people of Bangladesh are farmers. Million of farmers form the backbone of agriculture of this country. Livestock and poultry in Bangladesh are firmly integrated into the economic structure of farm and village life. Increasingly livestock and poultry enterprises are playing an important role in the elimination of poverty and creating employment and by removing malnutrition problems from the country. According to FAO (1989), Bangladesh have 89 million chicken but according to report of Department of planning of livestock services, Bangladesh had 89.9 million chicken in 1991 which has increased to 124.37 million in 1993 (Ahmed, 1994) which consists of indigenous, Australop, Rhode Island Red, White leghorn and ISA Brown. Increasingly, poultry enterprises are now being recognized as the key elements which contribute to the rural income. Live stock and poultry sector are responsible for about 6.5% of the country’s GDP (Ahmed, 1994). According to FAO (1998), there were 153 millions of native chicken, in our country commonly called native chicken. Bangladesh has now 0.127 millions of broiler farms both in small and large scale. (Rahman et al., 2003) However, some diseases such as colibacillosis, Gumboro etc. are the common constraints in developing the poultry farms in Bangladesh. These diseases affect the immune system and cause disorganization of the histological structures of the system concerned leading to poor production of meat and egg and even morbidity and mortality rate of the chicken increase significantly and hampers the development of farms. The Gumboro viruses primarily affect the B-lymphocytes of the bursa of Fabricius and other lymphoid tissues (Thymus, spleen and cecal tonsils) and mucosal immune system (lymphoid system of the gastrointestinal, Respiratory and oviduct) of the chicken. The lymphoid system of fowl is consisting of unique organs and divided into two morphologically and functionally distinct components (Cooper et al. 1965, 1966). The lymphoid tissue of the chicken is divided into “central” and “peripheral” tissues. The primary sites for the development of lymphocytes are central one, e.g.; the thymus and bursa of fabricius. The peripheral or secondary lymphoid tissue apparently depends on the central lymphoid tissue for their origin, development and function. In birds, the peripheral lymphoid tissue includes the spleen and all the mucosa-associated lymphoid tissue (MALT), including respiratory tract, Urinary tract, and alimentary tract with cecal tonsils (Getty, 1975; Bach, 1978). An obvious characteristic of the lymphoid tissues of mammals and birds is that they are densely populated with the lymphocytes. This is because they are involved with the lymphocyte production, immune responses or both of these processes occurring at the same time (Cormack, 1987). Lymphocytes form nodules in the lymphoid organs, and found scatteredly and homogenously in the mucosa-associated tissue. When the lymphocytes arrive in the tissues or organs, they become plasma cells and start to synthesize immunoglobulins. In chicken, the digestive system, respiratory system, urinary system and the reproductive system are mainly lined by mucosa, which forms a barrier between the external and internal environments.They encounter many antigens in general. Moreover, nonspecific mechanisms such as a continuous layer of epithelial cells, mucus and extreme PH values are also playing role in defense system. These mucosae contain several well defined lymphocytes that respond specifically to invading antigens which are called mucosa associated lymphoid tissue (MALT). When mucosa is exposed to foreign antigens, the mucosa associated lymphoid tissues (MALT) act as a source of lymphocytes, polymorphonuclear leukocytes, plasma cells and macrophages. This tissue plays an important role in immunological response to viruses as well as helps to induce immunity after oral immunization (Arai et al., 1988; Stitz, 1994). Immune competent cells including lymphocytes, plasma cells and macrophages have the ability to develop an immune response following exposure to antigens (Anderson, 1989). Lymphocytes are distributed homogenously in lymphatic nodules in the mucosa associated lymphoid tissues. Infectious bursal disease has been of great economic importance for the developing poultry industry (Alkhalaf, 2009). The infectious bursal disease virus (IBDV) at first infects (replicates) immune competent cells (lymphocytes and macrophages) in the mucosa associated lymphoid tissues of the duodenum, jejunum and cecum and subsequently replicates in the immature B-lymphocytes of Bursa of Fabricius and causes immunosuppression in chicken (Breytenbach, 2003). This immunosuppression prevents birds from optimally responding to vaccines (Winterfield and Thacker, 1978). The distribution of immune competent cells of the mucosa-associated lymphoid tissues (MALT) and other major lymphoid organs of the chicken have previously been reported (Vervelde and Jeurissen, 1993; Khan and Hashimoto, 1996; Khan et al., 1998; Khan and Hashimoto, 2001). Moreover, the histopathological changes and immunosuppressive effects on different lymphatic tissues of IBDV infected chicken have also been reported in Bursa of Fabricius (Tsukamoto, et al., 1995; Elankumaran et al., 2001; Alkhalaf, 2009), spleen (Hoque et al., 2001), thymus (Hoque et al., 2001), cecal tonsils (Elankumaran et al., 2001) and other non lymphoid organs like kidneys (Van der Sluis, 1994) and liver (Islam et al., 1997; Chowdhury et al., 1996). All of the mucosa associated lymphoid tissues morphologically similar and tend to produce IgA (McDermott and Bienenstock, 1979) together with the spleen and Lymphnodes, comprise the peripheral immune systems in animals. From the available literature, it is revealed that a few anatomical study of the MALT has been taken in the chicken of high yielding breed. Therefore the present work has been undertaken: •	To study the gross changes of lymphoid organs and mucosa associated lymphoid tissues(MALT) •	To study the distribution of lymphocyte in the digestive, respiratory, urinary and reproductive tract. •	To explore a comparison of distribution of lymphocyte between control and vaccinated group. However, relatively little information is available regarding the changes in number and distribution of lymphocytes in the mucosa-associated lymphoid tissues (MALT) of IBDV infected chicken. It is expected that the present studies will provide valuable information about population and distribution of lymphocytes in MALT of IBDV infected chickens which will be helpful to the poultry anatomist, immunologist, pathologists, researchers and breeders as well.