Secondary immunodeficiency: HIV, malnutrition, drugs, asplenia !

Topic

Most weak immune systems are acquired, from HIV, poor nutrition, medicines, cancer or losing the spleen, not inherited.

Updated 2026-11-01

See it in 3D: Spleen

Key points

HIV destroys CD4 T cells; AIDS is defined by a CD4 count below 200 cells per microliter or an AIDS-defining illness.
Protein-energy malnutrition mainly impairs T-cell function and the thymus; it is the leading cause of immunodeficiency in the world.
Asplenia (surgical, or functional as in sickle cell disease) raises the risk of overwhelming sepsis by encapsulated bacteria; Howell-Jolly bodies on the smear.
Corticosteroids lower lymphocytes and eosinophils, raise neutrophils and blunt fever; they can trigger Strongyloides hyperinfection and Pneumocystis pneumonia.
Anti-TNF biologics reactivate latent tuberculosis: TB screening (tuberculin skin test or IGRA) comes before starting them.
CLL and multiple myeloma lower functional antibodies; diabetes, kidney failure, cirrhosis and old age also weaken defenses.

What it is

A secondary immunodeficiency is acquired during life. Worldwide, malnutrition is the most common cause and HIV the best known; in hospitals, corticosteroids, chemotherapy, transplant drugs and biologics are frequent causes. Recognizing the cause predicts the infections to expect and the vaccines and prophylaxis that apply.

Main causes of acquired immunodeficiency

Cause	What fails	Typical infections	Clue or key test
HIV infection	CD4 T cells (cell-mediated immunity)	Pneumocystis, tuberculosis, Cryptococcus, Histoplasma, Toxoplasma, CMV, candidiasis	HIV test; CD4 count; viral load
Protein-energy malnutrition	T cells, thymus, phagocytes, complement, barriers	Severe measles, diarrhea, pneumonia, tuberculosis	Weight for height, albumin; often with micronutrient lack (zinc, vitamin A)
Drugs (corticosteroids, chemotherapy, transplant drugs, biologics)	Depends on the drug: neutrophils, T cells, B cells	Bacterial and fungal infections in neutropenia; Pneumocystis; TB reactivation with anti-TNF	Drug history; blood count
Asplenia (splenectomy, sickle cell disease)	Clearance of opsonized bacteria; IgM memory B cells	Overwhelming sepsis by pneumococcus, meningococcus, Haemophilus; severe malaria and babesiosis	Howell-Jolly bodies on the blood smear
Blood cancers (CLL, multiple myeloma)	Functional antibodies (hypogammaglobulinemia)	Recurrent pneumonia by encapsulated bacteria	Immunoglobulins; protein electrophoresis
Diabetes, kidney failure, cirrhosis, old age	Neutrophil function, barriers, complement	Skin and urinary infections, mucormycosis in ketoacidosis, spontaneous bacterial peritonitis	Glucose and HbA1c; kidney and liver tests

Clinical notes

In Colombia, tuberculosis and histoplasmosis are frequent opportunistic infections in people with advanced HIV.
People without a functioning spleen receive pneumococcal, meningococcal and Haemophilus influenzae type b vaccines, ideally before a planned splenectomy.
Before high-dose or long courses of corticosteroids, people who lived in tropical areas are often tested or treated for Strongyloides.

Test yourself

Think of the answer, then tap the question to see it.

What is the most common cause of immunodeficiency worldwide?

Protein-energy malnutrition, which mainly impairs T-cell immunity.

Which CD4 count defines AIDS in a person with HIV?

A CD4 count below 200 cells per microliter, or the presence of an AIDS-defining illness.

What finding on the blood smear suggests asplenia?

Howell-Jolly bodies, nuclear remnants in red cells that the spleen would normally remove.

Which infection must be ruled out before starting an anti-TNF biologic?

Latent tuberculosis, with a tuberculin skin test or interferon-gamma release assay (IGRA).

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See it in 3D

The structures of Durgical's 3D anatomy where it is found.

Spleen

Microorganisms

← All of immunology

Educational content on the immune system; not a treatment or individual vaccination guide and no substitute for a health professional's advice. No doses are given.

Sources: Immunodeficiency diseases (MedlinePlus, U.S. National Library of Medicine, 2026); About HIV (Centers for Disease Control and Prevention (CDC), 2026); Spleen removal (MedlinePlus, U.S. National Library of Medicine, 2026); Risk Factors for Meningococcal Disease (Centers for Disease Control and Prevention (CDC), 2026).

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Representative model, for educational purposes only.