I have read on the web that having Rh negative blood protects you from getting AIDS. Is this true?
-A curious adult from California October 14, 2010 I have found no reliable, scientific evidence anywhere that being Rh negative protects anyone from developing AIDS. None. There is no credible science to back up this claim. So for anyone out there who is Rh negative, please take all of the usual precautions. You get no protection from having this blood type. Which isn't surprising when you think about it. From a scientific point of view, it would be really weird if having Rh negative blood did give protection. After all, Rh negative has to do with red blood cells and AIDS has to do with white blood cells. It is very hard (although not impossible) to come up with ways for something in red blood cells to affect AIDS. Now this isn't to say that there aren't people who are less likely to get AIDS. There are. But as we might expect, these folks have genetic differences that affect their white blood cells or how they work. (Click here to learn more.) It is also important to emphasize that none of these genetic ways that protect people from getting AIDS is 100%. People with the "right" genetics can still be infected, it is just less likely. From a quick tour of the web, it looks like this rumor has gained a bit of strength lately based on an old study from an Indian journal, a patent, a misunderstanding of a Discovery Channel news story, and a misunderstanding of recent research article in the journal Blood. What I'll do for the rest of the answer is go over each in a bit of detail to explain the misunderstanding and/or to talk about why the evidence is really not that convincing. But before I do that, I want to emphasize again that Rh negative people are not resistant to HIV, the virus that causes AIDS. There are definitely many examples of people who are Rh negative and are suffering from AIDS. These sorts of viral internet rumors are a boon for HIV. The internet variety will get a certain group of people doing risky things because they think they are protected when they are not. These folks will be at an increased risk for infection and some will die. Indian Army Study too Small The first nugget of evidence is a study done in India in 1996 that claims that people who have Rh negative blood are less likely to get AIDS. This study was way too small to give meaningful results on its own. The study was done on 404 members of the Indian military, 104 of whom were HIV positive. The results were that 5% of the uninfected group was Rh negative and only 1.9% of the infected group was. First off, it is obvious that Rh negative folks can be infected by HIV. The number of infected Rh negative people in this study was not zero. But the major problem with this study is the small numbers involved. There are just too few Rh negative people to come to any real conclusions. The group without HIV (the control group) had 300 people and the group with HIV had 104 people. These numbers aren't that bad but because Rh negative blood is very uncommon in India, the control group only had 15 people with Rh negative blood and the HIV group had 2. These are the numbers the 5% and the 1.9% are based on. These numbers are way too small to be statistically significant. And frankly, the 5% number is surprisingly high. A truly random group of Asians would have numbers closer to 1% as Rh negative blood is very rare there. This is the kind of thing that can happen when you are dealing with very small groups. Simple chance will cause huge swings. This is why it is so important to include the margin of error in a study. My guess is that in this study, the margin of error would be more than the 1% needed to make the study meaningful. What this means is that this study is not enough on its own. Which is how science often starts out. Scientists do a small study and see something interesting. They then do a larger study and see if the result still stands up. When there is a small study like this one and no published follow up study, that often means that the follow up study didn't work. My guess is that the researchers did a follow on study and the results did not hold up. In any event, this is not evidence that Rh negative people are less likely to get AIDS. The study is just too small to draw any conclusions. Sayal SK et al. "Study of blood groups in HIV seropositive patients." Indian Journal of Dermatology, Venereology, and Leprology. 1996 Vol 62, Issue 5, pp. 295-297 The RhoGAM Patent Another supposed bit of supporting evidence is a patent that claims to use RhoGam to slow down the progression of AIDS. RhoGam is a medicine given to pregnant women with Rh negative blood who are carrying an Rh positive child. In these cases, mom's blood can develop antibodies that attack the baby's blood. This leads to something called hemolytic disease of the newborn (HDN) which can cause serious problems for the baby. Some babies even die from it. RhoGam binds and destroys any of the baby's blood cells that happened to have ended up in mom's blood. This prevents her from making the antibodies against Rh positive blood which might harm the baby. Even if RhoGam did slow down the progression of AIDS, that doesn't say much about AIDS and having Rh negative blood. Most Rh negative people don't have antibodies to Rh positive blood and Rh positive people certainly don't. So even if this is true, it doesn't tell us a whole lot (although it might be an interesting treatment for Rh negative people with HIV). It is also important to note that these results, like the previous study's, might not hold up under scrutiny. This is pretty common with patents. The science of patents is almost always preliminary. It is used less to rigorously prove something and more to put a stake down on something that might be true. Usually further work is needed to really nail down the results. And given the huge market and profits that HIV presents, if RhoGam slowed HIV progression it would be used right now or at the very least in clinical trials. Again, though, this doesn't have a lot to do with being Rh negative and AIDS progression. So this evidence tells us very little about HIV and Rh negative blood no matter if the science holds up or not. CCR5 is not Rh A story that received a lot of press recently reported that a man who received a bone marrow transplant was cured of his AIDS. This story appears to be true (click here to learn more). But this story has nothing to do with blood type or being Rh negative. Instead, it has to do with the CCR5 gene. The CCR5 gene has the instructions for a protein called CCR5. This protein forms part of the doorway that lets HIV into certain white blood cells. People who only have a version of the CCR5 gene called delta-32 are much less likely to be infected by HIV. And so they are less likely to end up with AIDS. This makes sense since people with the delta-32 version don't make any CCR5 protein. The front door to the white blood cell is now missing and so HIV needs to find some other way to get in. These ways are harder which is why these folks are more resistant to HIV. The person in this story received a bone marrow transplant from a donor with the delta-32 version of the CCR5 gene. His white blood cells now had no front door and so HIV could not get in. He has too little virus to detect. The CCR5 gene, though, has nothing to do with Rh factor. They are separate genes found on separate chromosomes. So to reiterate, this result has nothing to do with blood type. Pk is not Rh A recent report from the journal Blood did show a connection between blood type and risk for getting AIDS. But the blood type had nothing to do with the Rh factor. There are lots of different factors stuck to the outside of our cells. We hear about ABO and Rh factors because our immune systems usually react very strongly against them. This study looked at a much less well known factor called Pk. Some people's cells are littered with Pk while other people have little or none. The researchers found that cells that had lots of Pk were resistant to some strains of HIV. This result makes a lot more sense that anything to do with Rh because Pk is found on both red and white blood cells. However, again, don't get tested for Pk and then turn reckless if you have a lot of it. The studies were only done in a Petri dish in the lab so we don't know if it will hold up in the real world. And again, while it might lower the chances that someone will be infected by HIV, it does not lower those chances to zero. So even if true, it is no magic bullet -- it may just save you from an otherwise tragic mistake. The researchers also only looked at a few strains of HIV. As we talk about here, there are lots of different strains which may be more or less bothered by Pk. But whatever the final outcome, this again has nothing to do with Rh negative blood. There is no evidence that Rh negative blood affords any protection against HIV infection or AIDS progression. Period. Lund N et al. "The human Pk histo-blood group antigen provides protection against HIV-1 infection." Blood. 2009 May 14, pp. 4980-4991.

More Information

Rh is on the cell on the left.
HIV infects cells like the
one on the right.

HIV comes out of white blood
cells not red ones.