Veterinary Immunology and Serology

INTRODUCTION- ADAPTIVE IMMUNITY

• Adaptive immunity is specific for different microbial and non-microbial antigens and increased by repeated exposures to antigen. 
• Adaptive immunity when mediated by B-lymphocytes is called humoral immunity and when mediated by T lymphocytes  is called cell mediated immunity. 
• The T lymphocytes circulate throughout the body, passing continuously from vascular to lymphoid circulation and through the lymphoid organs and tissues.  B-lymphocytes do not re-circulate and mainly concentrated in spleen and lymphoid organs.
• In contrast to innate immunity, when immunity develops as a response to infection and adapts to the infection, it is called adaptive immunity.
• Adaptive immunity has an extraordinary capacity to distinguish among different closely related microorganisms or molecules and hence it is called specific immunity and provides defense activity with higher magnitude.
• Cardinal signs of immunity are specificity, diversity, memory and recognition of self and non-self. Innate immunity is phylogenetically the oldest system of host defense and adaptive immune system evolved later.