Secondary Immunodeficiencies: Clinical Immunology for Infectious Disease Specialists

Abstract: Secondary immunodeficiencies (SIDs) are acquired disorders of immune function arising from extrinsic insults to an otherwise intact immune system. Unlike primary immunodeficiencies, which are heritable, SIDs are far more prevalent, and encompass a broad spectrum of etiologies including infection, malignancy, malnutrition, metabolic disease, and iatrogenic causes. Among the latter, B cell depletion therapy has emerged as a clinically significant and increasingly utilized modality in the management of autoimmune disease, hematologic malignancy, and transplant medicine. This paper presents a structured review of secondary immunodeficiency states with particular attention to the mechanisms, clinical indications, immunological sequelae, infectious complications, and management strategies associated with B cell depletion therapy.