(3) Chapter 19: Disorders of Immune System

What are the two major types of immune deficiency?

Congenital (primary; present at birth due to genetic defects) and acquired (secondary; develops later from disease or treatment).

What is DiGeorge syndrome (thymic dysplasia)?

A congenital immune deficiency in which the thymus fails to develop, resulting in little or no T-cell (cell-mediated) immunity. It is often fatal in childhood.

What is Severe Combined Immunodeficiency (SCID)?

A congenital disorder in which both cell-mediated and antibody-mediated immunity are absent, leaving patients with virtually no functional immune system.

How can congenital immune deficiencies be treated?

Fetal thymus transplant, bone marrow (hematopoietic stem cell) transplant, and gene therapy.

What is artificial acquired immune deficiency?

Immune suppression caused intentionally by immunosuppressive drugs, such as after organ transplantation or for severe autoimmune diseases like psoriasis.

What is natural acquired immune deficiency?

Immune deficiency caused by disease, especially HIV infection.

Besides HIV, what conditions can cause acquired immune deficiency according to the lecture?

Hodgkin lymphoma (suppresses T-cell immunity) and removal of the spleen (reduces antibody-mediated immunity because the spleen contains many B cells).

Why are nude mice used in research?

They lack a thymus and therefore lack cell-mediated immunity, making them useful for cancer, transplantation, and immunology research.

What type of virus is HIV?

A Lentivirus and retrovirus with two positive-sense RNA strands, reverse transcriptase, integrase, a phospholipid envelope, and glycoprotein spikes.

Which cells are primarily infected by HIV?

Helper T (CD4) cells; HIV also infects macrophages and dendritic cells.

What receptors are required for HIV attachment?

HIV binds the CD4 receptor and also requires a co-receptor before fusion and entry into the cell.

Describe HIV entry into a host cell.

Glycoprotein spikes bind receptors, the viral envelope fuses with the cell membrane, uncoating occurs, and reverse transcriptase and integrase begin replication.

What is the role of reverse transcriptase in HIV?

It converts viral RNA into DNA.

What is the role of integrase in HIV?

It inserts viral DNA into the host cell's DNA, forming a provirus.

Compare active and latent HIV infection.

Active infection produces new viruses that bud from the cell. Latent infection occurs when viral DNA is integrated into the host genome as a provirus and no new viruses are produced.

How long can HIV latency last according to the lecture?

About 10 years.

How does HIV-2 differ from HIV-1?

HIV-2 (common in West Africa) has a shorter latency period, lower viral load, and lower mortality than HIV-1.

Why are macrophages important HIV reservoirs?

HIV can persist inside macrophages as proviruses or complete viruses hidden from the immune system and later become active again.

Describe the three clinical phases of HIV infection.

Phase I: asymptomatic or persistent lymphadenopathy. Phase II: symptomatic with steadily declining helper T cells. Phase III: clinical AIDS with CD4 count below 200 cells/µL.

What is the normal helper T-cell count?

Approximately 500–1500 cells/µL.

When is HIV classified as clinical AIDS?

When helper T-cell (CD4) count falls below 200 cells/µL.

What happens to viral load during HIV infection?

It peaks shortly after infection, decreases as the immune response develops, remains relatively stable during latency, then rises sharply as AIDS develops.

What is seroconversion?

The appearance of detectable antibodies against HIV in the blood, usually about 1–3 months after infection.

What are the major signs of Phase II HIV infection?

Persistent fever, persistent diarrhea, oral leukoplakia (white patches), oral thrush, shingles, and precancerous or cancerous cervical lesions.

What are common opportunistic infections seen in clinical AIDS?

Candida infections of the esophagus, bronchi, and lungs; tuberculosis; cytomegalovirus (CMV); Pneumocystis pneumonia; toxoplasmosis; and Kaposi's sarcoma.

According to the lecture, what usually causes death in AIDS patients?

Secondary opportunistic infections and cancers rather than HIV itself.

Why does the immune system eventually fail in HIV infection?

The body cannot replace helper T cells as quickly as HIV destroys them.

What are the major antiviral targets used to treat HIV?

Fusion, reverse transcriptase, integrase, protease, and viral release.

What does fusion inhibition accomplish?

It prevents HIV from fusing with the host cell membrane and entering the cell.

What does reverse transcriptase inhibition accomplish?

It prevents HIV from converting RNA into DNA.

What does integrase inhibition accomplish?

It prevents viral DNA from integrating into the host genome.

What does protease inhibition accomplish?

It prevents viral protein processing and viral maturation.

According to the professor, what should you memorize about HIV medications?

Know the viral targets (fusion, reverse transcriptase, integrase, protease, and release) and what blocking each target accomplishes rather than memorizing every drug name.