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Chimps, AIDS, And Immunity
Anonymous Coward writes "Researchers at the Biomedical Primate Research Center in The Netherlands have come up with a theory as to why modern chimps don't develop AIDS and its variants.
The chimps in the study were found to share a usually uniform cluster of genes in the area that controls their immune systems' defenses against disease. This lack of genetic diversity suggests that a lethal sickness attacked chimps in the distant past.
The theory postulates that approximately 2 million years ago an AIDS-like epidemic wiped out a large portion of the chimpanzee population. Those that survived developed an immunity to AIDS and its variants.
If this theory holds true it may explain why some humans who are repeatedly exposed to HIV don't get sick."
It is actually rather simple why certain people can be repeatedly exposed to HIV and not become productively infected. HIV requires its target cells have two cell surface proteins in order to infect it. One is the basic CD4 T cell receptor. The other is one of two different types of chemokine receptor. There is the CXCR4 and CCR5 receptors. The names derive from a common amino acid motif found in these receptors in most people: for CXCR4 it is cysteine-any amino-cysteine-arginine. For CCR5 it is cysteine-cysteine-arginine. Most of the people who appear immune to the infection contain a mutation in the CCR5 receptor (I'm not familiar with the CXCR4 receptor vis a vis mutations and infection resistance). Thus, HIV can bind to CD4 but because of the mutation in CCR5 it cannot complete the process and fuse with the cell. No fusion, no infection.
This common form of resistance doesn't require any cluster of genes nor any mysterious genetic variation or evolutionary alteration.
In Bushworld, they struggle to keep church and state separate in Iraq as they increasingly merge the two in America.
"Those that survived developed an immunity to AIDS and its variants. " ...Uh, IANA genetecist, but I THINK the way it works is that those that ALREADY had the peculiar genetic combination that would equip them to survive SIV where the ones that SURVIVED. Through their offspring this combination came to prevail in the population today...
AIDS is not something that just kinda turns up in your system one fine morning; is an epidemic that can be effectively prevented with some very basic safeguards.
Rape is a huge problem in Africa, especially in the kwa-Zulu Natal area that has been described as the 'epicenter of AIDS' now that Uganda has gotten things under control. AIDS really can just kinda turn up in your system one morning without you having any choice in the matter - for many people, it's often not as simple as wearing a condom and not sharing a needle.
I'm not a biochemist, but I can answer the second one: Sometimes. Gene mutations are belived to be random. The chimp doesn't have a SIV specific gene, it has a gene that causes certian types of protiens. The protien then allows certian immunities. It might happen that the gene only affects SIV, more likely it affects several things, which might or might not include HIV.
One of the early vacinations for small pox was bassed on cow pox, once infected by cow pox you were immune to small pox. So yes, one infection can make you resistant to a different one. However there are many different viriues. Most people get the flu every year, and each time they get one strain they become resistant to that and several other, however appearently not the one that strikes the next year.
There are too many random factors in immunities and genetics to really answer your second question, but I tried.