Phenotypic abnormality Abnormality of the immune system An abnormality of the immune system. HP:0003257 HP:0010986 Abnormality of the immune system HP:0003346 Immunological abnormality UMLS:C4021753 The immune system is composed of organs and interdependent cell types that collectively protect the body from infections and from the growth of tumor cells. The organs of the immune system comprise the bone marrow, the spleen, the thymus,the lymph nodes, and the cell types comprise B cells, T cells, natural killer cells, granulocytes,dendritic cells, and macrophages.