Medical Genetics 1 General Immunodeficiencies may be primary or secondary Primary immunodeficiency is classified into four main groups depending on which component of the immune system is deficient: B cells, T cells phagocytic cells, or complementMedical Genetics 1. General Immunodeficiencies may be primary or secondary. Primary immunodeficiency is classified into four main groups depending on which component of the immune system is deficient: B cells, T cells, phagocytic cells, or complement