Any disease-causing agent that we are exposed to (bacteria, virus, fungus, parasite, etc.)
Consists of skin and mucous membranes, physical barriers are our first line of defense against pathogens. Physical barriers are part of our non-specific immunity.
Also known as non-specific immunity, innate immunity consists of general physiologic responses (fever, inflammation, etc.) that can affect the entire body.
Also known as specific immunity, adaptive immunity is carried out by T & B lymphocytes and reacts to specific antigens of cells; adaptive immunity also produces memory cells to target the same pathogen if we are ever exposed to it again.