Some of you may have read that O negative people cannot get AIDS. Of course, regarding blood types and likelihood to contract the HIV virus there still is research to be done, but so far there has been no evidence that universal donors are protected from it.
So be careful and don´t assume that you are protected by your blood type regardless what it is!
See also: Can rh negative people get HIV/AIDS?
A recent article … found evidence that a certain, relatively uncommon, blood type may be associated with resistance to HIV infection. This blood type, which is not part of the more commonly discussed A/B/O or Rh groupings, is characterized by the amount of a protein known as Pk present on blood cells. In this small study, the blood cells of those individuals who had higher levels of Pk were found to be more resistant to infection by HIV. This genetic factor could explain some of the population variance in susceptibility to HIV and AIDS. This is not the first genetic factor that has been found to be associated with susceptibility to HIV. A mutation in the protein CCR5, that is found most commonly in certain European populations, also got some attention a few years back for providing resistance to HIV infection.
However, it could indeed be the case that rh negative people are less likely to become infected:
HIV infection has been reported to occur in select blood groups in some regions of the world. A study by Sayal et al. in India reported a preponderance for infection in group O Rh(D)-positive men and least among groups B positive and D-negative ones. However, a close examination of the results reveals insufficient statistical analysis rendering the differences statistically insignificant. Similar studies by Nneli et al.  and Dirisu et al.  suffered similar deficiencies. In these studies, group O positive individuals were thought to be highly susceptible, but again the studies lacked the statistical rigor to indicate the level of significance and have been contradicted by other investigators . A statistical interrogation of the data in each of the above case does not support the conclusion of statistical significance.
It would then appear that current scientific information does not support a potential role for ABO blood groups in HIV infection. In fact, evidence from other studies would suggest the contrary for group O individuals. Since HIV virions have been shown to acquire the blood group antigens of the infected individuals [2, 6, 42], such virions would be neutralized by naturally-occurring antibodies in group O individuals, thus offering protection in blood group-discordant couples . It is noted, however, that this protection will not be available if the source of infection was of a similar blood group. Moreover, given the apparently uniform risk of infection among ABO blood groups, it is doubtful if this neutralization is of any clinical consequence, especially with reference to HIV-1 infection. It remains to be demonstrated then whether HIV from blood group A or B is able to infect group O CD4 cells.
In a separate study, Abdulazeez and colleagues  working with HIV-1 and -2 reported a higher prevalence of HIV-2 (71.4%) compared to HIV-1 (7.1%) in the AB blood group and that Rh(D) positive (97.8%) was more susceptible than D negative (2.2%). However, these findings are yet to be confirmed by other investigators.
(Source: The Role of Red Blood Cells in Enhancing or Preventing HIV Infection and Other Diseases)
The first genetic mutation associated with HIV susceptibility was identified in the mid 1990s. Known as the CCR5-Delta32 mutation, it seems to confer strong resistance to infection by HIV. This gene mutation is found most commonly in certain European populations, possibly because it was also associated with resistance to other diseases such as smallpox or the Bubonic Plague.
And also regarding Pk:
The role of ABO blood groups in infectious and non infectious diseases is well established. Much scientific evidence also exists to support the role of erythrocytes in binding viruses and facilitating infection of permissive cells. Some blood groups such as the Duffy type are implicated as candidate molecules. Other molecules such as the Pk blood group which are present in Caucasian populations have been shown to confer resistance to HIV infection. The study of blood groups in HIV infection may shed light on the dynamics of HIV epidemiology, especially in hard-hit SubSaharan Africa.
And as we all know, European populations in general have a higher percentage on an average than native populations of other continents.
If indeed the above bolded study turns out to be verified by other studies and Rh(D) positive (97.8%) was more susceptible than D negative (2.2%), that could mean that rh positive individuals are around 7 times more likely to contract the HIV virus than rh negatives.
We will keep you posted should more information come our way.
Until then: Don´t risk anything believing that you are protected by being D negative!