By Liz Highleyman

In the U.S., numerous epidemiological studies have shown that African-Americans have higher rates of HIV infection than people of other racial/ethnic groups, and the prevalence of HIV/AIDS in sub-Saharan Africa exceeds that in other regions of the world. While multiple socioeconomic and other factors play a role, experts have puzzled over the fact that blacks seem to be more likely to become infected with HIV even if they are equally or even less likely to engage in sexual and drug use practices that transmit the virus.

In 2007, investigators reported that human semen contains peptide fragments derived from an enzyme produced by the prostate gland. These fragments form amyloid fibrils or fiber structures -- dubbed "semen-derived enhancer of virus infection," or SEVI -- that appear to capture HIV particles and direct them to vulnerable host target cells.

As presented at ICAAC, researchers from Meharry Medical College in Nashville set out to assess the hypothesis that differences in the ability of SEVI to enhance infection might help explain differences in rates of HIV infection across racial/ethnic groups.

As background, they noted that the most recent Centers for Disease Control and Prevention (CDC) statistics indicate that African-Americans have the highest incidence of HIV cases in the U.S. -- approaching 50% -- despite the fact that they comprise about 12% of the total population.

The investigators collected semen samples from donors across multiple racial/ethnic groups: 50 African-Americans, 100 Caucasians, 10 Hispanics, 10 people of (east) Indian descent, and 10 people of Asian descent.

Semen was processed to yield SEVI precipitates, and physiological concentrations of either SEVI or an inactive peptide control were incubated with HIV (strain NL4-3) in laboratory cell cultures for 2 hours.

Results

	The researchers observed individual differences in SEVI-mediated effects on HIV infection, ranging from high enhancement, to no change, to inhibition.
	The ability of SEVI to facilitate HIV infection varied widely within each racial/ethnic group, and there were also some differences between the groups:
	African-Americans: 0.3 to 8.5 fold change in infection enhancement; Caucasian: 0.2 to 7.9 fold change; Hispanics: 1.2 to 7.0 fold change; Indians: 1.0 to 2.0 fold change; Asians: 0.1 to 1.0 fold change.
	SEVI from African-Americans, Caucasians, and Hispanics demonstrated the highest overall levels of enhancement.
	In contrast, SEVI from Asians tended to inhibit infection.
	Differences in infection enhancement between African-Americans, Indians, and Asians, as well as between Caucasians, Indians, and Asians, were determined to be statistically significant.
	Differences between African-Americans, Caucasians, and Hispanics, however, did not reach statistical significance.

"Results from these preliminary studies indicate that individual donor differences exist in the ability of SEVI to enhance in vitro HIV-1 infection of immortalized cells and SEVI may play a role in the racial health disparities associated with HIV-1 infection," the investigators concluded.

Furthermore, they indicated that they are aiming to develop agents to block interactions between SEVI, HIV, and host cells that potentially might be used -- perhaps in a microbicide, for example -- to prevent sexual transmission of HIV.

Meharry Medical College, Nashville, TN.

10/06/09

References
MN Madison and JEK Hildreth. Individual Donor Differences in the Ability of Semen-Derived Enhancer of Viral Infection (SEVI) to Promote HIV-1 Infection. 49th Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC 2009). San Francisco. September 12-15, 2009. Abstract H-1569.