Host Defense Mechanisms Against Infection By Larry M Bush, MD, FACP, Charles E Schmidt College of Medicine, Florida Atlantic University Reviewed / Revised Aug 2022 | Modified Sep 2022 View Patient Education Natural Barriers Against Infection Nonspecific Immune Responses (Innate Immune Responses) Specific Immune Responses (Adaptive Immune Responses) Host Genetic Factors Host defenses that protect against infection include Natural barriers (eg, skin, mucous membranes) Nonspecific immune responses (eg, phagocytic cells [neutrophils, macrophages] and their products) Specific immune responses (eg, antibodies, lymphocytes) (See also Overview of the Immune System.)