Human immunodeficiency virus antibodies, do you know?

Immunodeficiency virus is a very rare disease, but it is very harmful. Once infected, it will directly harm human health and even life safety. Therefore, people need to have a certain understanding of the immunodeficiency virus, including its morphological structure and coding genes, which are all worth slowly pondering and understanding.

1. Source

On March 4, 2015, scientists from multiple countries discovered that the four known strains of HIV all came from chimpanzees and gorillas in Cameroon. This is the first time that humans have completely identified all the sources of HIV strains.

There are four known strains of HIV: M, N, O, and P. Each has a different source. The most widely spread strains, M and N, have long been confirmed to come from chimpanzees, but the rarer O and P were only later confirmed to be from gorillas in southwestern Cameroon.

There have been only two cases of type P in the world so far, and only 100,000 people with type O, mainly concentrated in Central and West Africa.

2. Morphological characteristics

1. Morphological structure

The human immunodeficiency virus is about 120 nanometers in diameter and is roughly spherical. The viral outer membrane is a lipid envelope that comes from the host cell and is embedded with viral proteins gp120 and gp41; gp41 is a transmembrane protein, gp120 is located on the surface and binds to gp41 through non-covalent interaction. Inward is the spherical matrix (Matrix) formed by protein p17 and the semi-conical capsid (Capsid) formed by protein p24. The capsid shows high electron density under an electron microscope. The capsid contains the viral RNA genome, enzymes (reverse transcriptase, integrase, protease), and other components from the host cell (such as tRNAlys3, which serves as a primer for reverse transcription).

2. Coding genes

The viral genome consists of two identical positive-strand RNA strands, each approximately 9.2-9.8 kb long. At both ends are long terminal repeats (LTRs), which contain cis-regulatory sequences that control the expression of the provirus. It has been demonstrated that LTR contains promoters, enhancers and negative regulatory regions. The sequences between LTRs encode at least 9 proteins, which can be divided into three categories: structural proteins, regulatory proteins, and auxiliary proteins.

1. The gag gene can encode a polymer precursor protein composed of about 500 amino acids, which is hydrolyzed by proteases to form P17 and P24 nucleoproteins, protecting RNA from damage by external nucleases.

2. The Pol gene encodes the polymerase precursor protein, which is cleaved to form protease, integrase, reverse transcriptase, and ribonuclease H, all of which are necessary for viral proliferation.

3. The env gene encodes a precursor protein of approximately 863 amino acids and is glycosylated into gp160, gp120 and gp41. gp120 contains a neutralizing antigenic determinant cluster, and it has been proven that the HIV neutralizing antigenic epitope is located on the gp120 V3 loop. The V3 loop region is an important functional region of the envelope protein and plays an important role in the fusion of virus and cells. gp120 is non-covalently linked to the transmembrane protein gp41. gp41 fuses with the target cell, allowing the virus to enter the cell. Experiments have shown that gp41 also has strong antigenicity and can induce antibody response.

4. The protein encoded by the TaT gene can bind to LTR to increase the transcription rate of all viral genes, and can also promote the translation of viral mRNA after transcription.

5. The Rev gene product is a cis-activating factor that can de-inhibit the cis-acting repression sequence (Crs) in env and gag, enhance the expression of gag and env genes, and synthesize the corresponding viral structural proteins.

6. The protein P27 encoded by the Nef gene has a negative regulatory effect on the expression of HIV genes, thereby delaying viral replication. This protein acts on the LTR of HIV cDNA and inhibits the transcription of integrated viruses. It may be necessary for HIV to maintain a persistent presence in the body.

7. The Vif gene is not essential for HIV, but may affect the infectivity of free HIV, the production of virions, and transmission in the body.

8. The VPU gene is unique to HIV-1 and is essential for the effective replication of HIV and the assembly and maturation of virions.

9. The protein encoded by the Vpr gene is a weak transcriptional activator that plays a certain role in the reproductive cycle in the body.

The genetic structure of HIV-2 is different from that of HIV-1: it does not contain the VPU gene, but has a VPX gene of unknown function. Nucleic acid hybridization method was used to examine the nucleotide sequences of HIV-1 and HIV-2, and only 40% of them were identical. The antibodies produced by the body stimulated by the env gene expression product have no cross-reaction.