For so many occasions, we have seen married couples that present with varying HIV serological status.

I heard of a couple in Cyangugu that had stayed together for 30 years with the Man exposed to HIV and the woman stayed sero-negative. They produced HIV-free children and for several occasions both the mother and children have tested negative to HIV.

There are also circumstances where you find a HIV negative man with the wife having died of HIVcomplications several years ago. This man could marry another sero-positive woman and have children.

Such couples normally give birth to HIV free off springs by way of Prevention of Mother to Child Transmission (PMTCT).

It should also be strongly noted that discordance is not related to blood groups and there is no particular blood group which protects people from being infected with HIV.

The fact that some people can resist being infected with HIV, despite being exposed to the virus over a long period has offered scientists much work and pending clinical investigations concerning HIV infection.
However people in discordant relationships are at a higher risk of developing HIV than the general population. Such people are advised to use condoms correctly and consistently whenever they have sex instead of thinking they are immune to HIV. This is because they can easily become infected with HIV any time.
People in sexual relationships should go for HIV tests with their sexual partners. They should not imagine they are of the same status as their partners.

Scientists have developed vaccines using their understanding though there is still pending evidence on what causes protective immunity against a targeted disease. With HIV, however an understanding of protective immunity is lacking, hampering the development of a vaccine and other drugs to combat the virus. 
 
For example, 15 years ago investigators tracked groups of commercial sex workers in Kenya who did not become infected with HIV despite repeatedly having sex without condoms.

The major aim of the study was to investigate and analyze reasons why some people were exposed to the HIV virus and did not get infected, whereas others would easily get infected so quickly when exposed to any HIV causative agent.

This information is very important because if scientists can understand what constitutes and results in protective immunity against HIV, they may be able to replicate it through vaccines.

Until few years ago, scientists proved that the difference in infection with HIV amongst the population is linked with the presence or absence of receptors found within our body. These receptors are named and labeled as CCR5 and CXCR4 receptors.

These two new proteins found on immune cells, play a key role in understanding how HIV infects cells. Immune cells are cells responsible for defense mechanism of our body.

Though these discoveries may not have immediate impact on people with HIV, they may lead to important advances in HIV treatment, prevention and research in the future.

The new discoveries reveal that people without CCR5 and CXCR4 receptors hardly get infected with HIV even after a long exposure. The commercial sex workers were found to have no receptors and this is why they were not found to be infected with the disease after having unprotected sex for long periods with HIV positive men.

CCR5 is present on a broad range of cells that can be infected by HIV. CXCR4 on the other hand, is primarily found on immune cells such as CD4+ cells and only appears to serve as a doorway for certain types of HIV.

CCR5 appears to be important for NSI strains of HIV (the strains most common in early disease), while CXCR4 appears to be more important for SI strains (a more aggressive strain seen in some people with more aggressive disease).

NSI (non-syncitium inducing) strains of HIV are the most common sexually transmitted form of the virus. This type of HIV preferentially infects cells found in the skin.

The SI (syncitium inducing) strain of HIV is more aggressive and its prevalence correlates with more rapid disease progression. Additionally, anti-HIV drugs generally have less activity against SI strains of HIV. The most obvious difference between someone with an NSI versus an SI strain, however, is that people with an SI strain experience more rapid decline in CD4+ counts, as the SI virus preferentially infects and destroys these cells. Also, people with the SI strain tend to have at least a 3 to 5 fold increase in the rate of disease progression.

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