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Which immune system components can be affected by immunodeficiency?

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immune system disorder False-color scanning electron micrograph of a T cell infected with HIV (human immunodeficiency virus), the agent that causes AIDS (acquired immunodeficiency syndrome).

Immunodeficiency disorders occur when there are defects in the body's immune mechanisms, impairing its ability to resist infection. These defects can affect several critical components of the immune system, including:12

Lymphocytes: This includes both T cells and B cells, which are essential for cell-mediated and humoral immunity, respectively.123
Antibodies: Also known as immunoglobulins, these proteins are produced by B cells to neutralize or destroy foreign antigens.234
Other Leukocytes: Various white blood cells, such as scavenger cells (phagocytes), can be affected, potentially hindering the body's ability to ingest and break down pathogens.124
Complement System: These proteins work in conjunction with other immune responses to help clear pathogens.12

In severe conditions like severe combined immunodeficiency (SCID), multiple components of the immune system are disrupted simultaneously due to a failure of precursor cells to differentiate into functional T or B cells.24