Some aspects of the application of immunostimulants and a critical review of method for their evaluation

Many occasions arise in fish culture in which it is desirable to enhance the immune response. These include strengthening the normal immune response in order to enhance protection and reduce immunosuppressive conditions. Several categories of immunostimulators can be classified by their origin and mode of action: (1) bacteria and bacterial products; (2) complex carbohydrates; (3) vaccines ('paramunity inducer'); (4) immunoenhancing drugs; (5) nutritional factors; (6) animal extracts; (7) cytokines; (8) lectins, plant extracts. In this paper, the importance of many immunostimulatory substances and their effects on fish immune systems are discussed. Two main procedures for evaluating the efficiency of an immunostimulant are: (a) 'in vivo', e.g. protection tests against fish pathogens; (b) 'in vitro', e.g. measurement of the efficiency of cellular and humoral immune mechanisms; the efficiency of these different evaluation methods is discussed. Attention is focused on the lymphocyte proliferation test as an adequate method for providing a correct evaluation of cellular immune conditions which can be adapted together with the more commonly used parameters, such as phagocytosis and respiratory burst. The use of immunostimulants in the diets of marine fish and the evaluation of their effect on the immune system of fish are also discussed

Níveis crescentes de parede de levedura sobre a resposta imune celular e perfil hematológico de frangos de corte Cellular immune response and hematological parameters of broilers from different age broiler breeders, fed with a sorghum meal with different yeast wall levels

Um experimento foi conduzido para avaliar o efeito de níveis crescentes de parede de levedura e idade das matrizes reprodutoras sobre o peso dos órgãos linfóides, a resposta imune celular e o perfil hematológico de frangos de corte. Foram utilizados 3.360 pintos de corte da linhagem Cobb, distribuídos em delineamento inteiramente casualisado, em esquema fatorial 2x5, mais dois controles, sendo duas idades de matrizes (34 e 57 semanas de idade) e cinco níveis de suplementação de parede de levedura (zero, um, dois, três e quatro kg de parede de levedura/tonelada de ração). A idade das matrizes influenciou a resposta de todas as variáveis. A inclusão de 3kg de parede de levedura/tonelada de ração promoveu, na progênie de reprodutoras de 57 semanas, reação inflamatória mais intensa quando comparada a dieta controle, no entanto não houve aumento significativo no número de heterófilos e linfócitos circulantes. Conclui-se que a utilização da parede de levedura associada ao sorgo ou não em rações de frangos de corte ainda necessita de estudos complementares, que incluam, por exemplo, os componentes purificados da parede de levedura (MOS e ß-glucano).<br>An experiment was carried out to evaluate the effect increasing levels of yeast wall and broiler breeders' age levels on lymphoid organs weight, cellular immune response and hematological parameters in broilers. A total of 3,360 Cobb broilers were allotted, in a completely randomized design and a 2x5 factorial arrangement, and two controls, compound of two broiler breeders age (34 and 57 weeks of age) and five yeast wall levels (zero, one, two, three and four kg of yeast wall/ton of diet). Broiler breeders' age affected all studied variables. The inclusion of 3kg of yeast wall/ton of meal increased, at 57 weeks age broiler breeders, more intense inflammatory reaction when compared to control diet; however the circulated heterophils and lymphocytes numbers were not increased. In conclusion, the use of yeast wall, associated or not to sorghum on broilers diet still needs complementary studies, for example, purified components of yeast wall (MOS and ß-glucano)