Veterinary Immunology and Serology

INTRODUCTION-IMMUNE SYSTEM

• When an animal is born, it emerges from mother’s womb to a new external environment where microorganisms are present.
• To combat the micro- organisms, Immune system must be developed.
• In some species like mice, gestation period is short and immune system is not fully developed at the time of birth but in major domestic animals, gestation period is long and immune system is fully developed at birth although not fully functional.
• Development of immune capability depends on antigenic stimulation but in very early days they are protected by passive transfer of antibody from mother.
• The development of immune system in mammalian fetus follows a consistent pattern.
• Thymus is the first lymphoid organ (primary lymphoid organ) to be developed followed by secondary lymphoid organs.
• Primary lymphoid organs are the organs where differentiation and maturation of lymphocytes takes place without antigenic stimulation. In secondary lymphoid organs, antigenic stimulation of B and T lymphocytes results in specific immune reaction.
• Immunoglobulin containing cells develop soon after the appearance of spleen and lymph nodes but antibodies are found in late stage of fetal life. Capability to respond to antigen develops after the lymphoid organs appear.