ABSTRACT
A functioning immune system is not only essential to successfully protect the host from foreign or ‘non self’ antigens such as various infectious pathogens but also to prevent immune responses to ‘self’ antigens and emergence of autoimmune diseases. The recognition of self and -non- self-antigens is a function of both the inborn or innate immune system and the adaptive immune system. A functioning immune system represents a sequential and organized maturation and differentiation of the Hematopoietic Stem Cell (HSC). Primary or congenital immunodeficiency can thus be looked upon as a defect or block in the development and maturation of the immune system. A defect in the structure and/or function of the immune system results in a derangement of the host defensive system resulting in severe or recurrent infections. A normal immune system not only eliminates ‘foreign or non-self’ antigens but at the same time is tolerant to ‘self-antigens’.
