“A healthier bird produces an economic output” is the one phrase which every poultry producer would agree upon from their daily farming experiences. The poultry industry strives to achieve this healthier state through precise nutritional and management practices. In nature, the chicks are being exposed to various challenges like physical, environmental and infectious agents from the moment they are exposed to outside world, sometimes even before their arrival. Naïve immune cells of the chicks are being tested by these ‘n’ number of challenges. To combat these challenges, all birds are gifted with an active immune system. Thus, the productivity of a bird can be defined by its ability to react and overcome these challenges.
The need for an active immune system is to protect and prevent. The immune responses of a bird can be classified into two types, the innate (non-specific) and adaptive (specific) immunity. Innate immune reactions are the initial bodily reaction to any foreign particle, thereby preventing their entry, growth or development, and further to prepare the host for any adaptive responses if needed. Initially, the scientific community concentrated their research activities on adaptive immune responses due to the popularity of vaccination interventions and the ‘memory’ factor of it. Off late, many research groups are involved in understanding the basics of innate immunity and how to exploit it for the prevention of disease conditions and betterment of the bird’s performance.
The seed for innate immune response research activities was started by Iiya Machnikov with his studies on ‘phagocytosis’ phenomenon (cell eating) of macrophage cells, for which he was rightfully awarded the Nobel Prize in 1908. Later, various cells types like macrophages, eosinophils, neutrophils, dendritic, natural killer cells and even the epithelial cells were demonstrated to be associated with the innate immune system. Unlike adaptive immune cells, the receptors of these immune cells are germ-line encoded and are found to exist both in vertebrate and invertebrate species. More than 98 % of the living species in the world are known to survive only with an innate immune system, unlike the vertebrate animals that have the specialized adaptive immune system.
MODE OF ACTION OF INNATE RESPONSES
Innate immune response is recognized to be activated through the pattern recognition receptors (PRR’s) in the innate immune cells present as cytoplasmic or membrane-bound. The PRR’s can recognize exogenous antigens through their pathogen-associated molecular patterns (PAMP’s) like lipopolysaccharides (LPS), peptidoglycans or nucleotide structures of the invading pathogens. The innate responses are mediated through the chemokines and cytokines resulting in an acute phase or inflammatory reactions and subsequently presenting the antigens for the development of adaptive immunity.
IMMUNE CHALLENGES IN POULTRY
The poultry birds are continuously being exposed to numerous pathogens from viral, bacterial, fungal origins to various other foreign agents from their surroundings. Each pathogen entry is being handled by its immune system through multiple innate and adaptive immune mechanisms. If these pathogens could break through the innate responses, the avian immune system reacts better with an adaptive systemic response. Normal functioning of the specific immunity needs an active innate immune system, for processing and presenting of these foreign antigens to be handled through humoral or cell-mediated response of the body.
MODULATION OF INNATE IMMUNITY
For years, methods to improve the immune responses have engrossed the research interests among scientists. Until recently, immunological interventions other than the vaccine usage had been one of a less traveled path for improving the health. Though the vaccination and specific immunity boosters play critical roles in preventing the occurrence of diseases, the augmentation of innate immune responses at an early stage of lifespan will have long-lasting effects on the bird’s health status and its productivity. During the chick stage (0 to 14 days age group), innate immune cells like heterophils and macrophages are known to be less efficient in handling the disease threats.
Many research studies have established the upregulation of immune responses through toll-like receptor (TLR) ligands, direct-fed microbials (DFM) or cytokine-mediated activation for overcoming the immune shortages of poultry birds. Modulation of the innate immunity through any of these activation strategies would help the broiler birds in developing an efficient immune response, thereby supporting in its commercial performances.