HIV Pathophysiology

HIV's primary target is the CD4+ cell (also known as the helper T cell or Th) HIV primarily infects the CD4+ cells of the immune system, but it also attacks macrophages and central nervous system cells. Early on in the infection, the virus invades and multiplies in the lymphoid tissue which act as a reservoir for infection. This is the reason swollen lymph nodes are one of the clinical manifestations of HIV. The role of the CD4+ cell is to activate B cells and cytotoxic T cells during an immune response - without CD4+ cells, there would be no immune response. Interesting Fact: CD stands for Cluster of Differentiation and is a system developed in 1982 of naming surface molecules of white blood cells (leukocytes). A + or - symbol indicates whether a cluster of cells expresses or lacks a surface molecule. For example, a CD34+, CD31- cell is one that expresses CD34 but lack CD31.

HIV uses its 2 surface receptors to enter CD4 cells.

HIV has 2 protein surface receptors:

1. gp120
2. gp41

The gp120 receptor of HIV binds to the CD4 receptor of CD4 cells. Both HIV and CD4 cells also have co-receptors that aid in the binding - HIV's co-receptor is gp41 while CD4 cells can have either the CCR5 or the CXCR4 as a co-receptor.

Video animation clearly showing HIV binding to CD4 cells.

The most detailed 3D model of HIV to date.

HIV uses 3 enzymes to help it attack CD4 cells.

Recall that HIV is a retrovirus that carries RNA instead of DNA. Inside its cell membrane, it carries 2 strands of RNA and 3 viral enzymes.

HIV's 3 Viral Enzymes

1. Reverse transcriptase
Used to convert the single-stranded RNA into double-stranded DNA.
2. Integrase
Used to insert the viral double-stranded DNA into the genetic material (also double-stranded DNA) of the infected CD4 cell. Once HIV is integrated into the host DNA, it uses the cell's machinery to create viral proteins.
3. Protease
Used to cleave viral proteins into smaller strands so that it can be packaged into virions that includes the 2 single-stranded RNA and the 3 enzymes. These virions then bud from the host cell to infect other cells.

Test Yourself

Question: What 3 enzymes does HIV carry? Match the enzymes with its function.

Enzyme 1:

Enzyme 2:

Enzyme 3:

1. converts viral single stranded RNA into double-stranded DNA
2. combines HIV's genetic material into the host's genetic material
3. cleaves HIV proteins into smaller proteins for packaging into virions

See the answer.

HIV's 3 enzymes:

1. Reverse Transcriptase: A) converts viral single stranded RNA into double-stranded DNA
2. Integrase: B) combines HIV's genetic material into the host's genetic material
3. Protease: C) cleaves HIV proteins into smaller proteins for packaging into virions

Back to question.


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