This weeks’s papers from Boston labs

Pat McCaffrey

HIV blocked when entering new immune cell doorway

Researchers have identified an alternative route by which the human immunodeficiency virus enters some types of immune cells without multiplying and causing infection.

This discovery could help advance vaccine design, according to Harvard School of Public Health researchers Roberto Trujillo, Max Essex, Joseph Brain, and colleagues in their paper in the Proceedings of the National Academy of Sciences.

HIV typically invades immune cells by binding protein receptor molecules on the cells’ surface. The virus then multiplies rapidly, killing the cells and moving on to eventually destroy the immune system.

But the researchers found that when HIV binds carbohydrate-based receptors on the surface of one class of immune cells called macrophages, it gets shuttled down the scavenging pathway and ends up sequestered, unable to multiply and destined for destruction. Macrophages avidly take up and destroy many other kinds of microbes using these same receptors.

The results show that HIV can enter macrophages through two routes: the infectious route and the new, noninfectious route that may even help trigger an immune response to the virus. Future vaccines could be engineered to promote more HIV entry via the carbohydrate receptor.

The results may also shed light on why macrophages lose their ability to eliminate other pathogens in HIV-infected people. When the carbohydrate receptor is totally occupied with HIV, the results show, the macrophages aren’t able to clear other microbes. This interference might contribute to the opportunistic infections characteristic of AIDS.

Emotions make for tough moral choices

Would you throw an injured comrade from an overloaded lifeboat if that would ensure the survival of the rest of the group? What about killing one of your children to save the rest of the family? From a purely logical point of view, the answer to these moral dilemmas should be clear—sacrifice one to save many. But emotionally speaking, not many parents would feel that killing their child is the right thing to do.

There’s a physiological reason for that, according to new work from Marc Hauser and colleagues from Harvard University, the University of Southern California, Caltech, and the University of Iowa. The researchers have found that, in addition to the brain’s logical decision-making region, a part of the brain involved in social emotions like compassion, shame, and guilt is intimately involved in solving personal moral dilemmas.

Their study, published online this week in Nature, shows that people who have suffered damage to parts of the frontal lobe, which processes social emotions, consistently took a more coldly utilitarian view of difficult decisions, generally favoring the greater good over individual compassion.

The researchers compared six adults who had damage in their frontal lobes with normal people and with those who had suffered brain damage in other areas. They presented the subjects with dozens of scenarios, ranging from simple decisions (buy a new computer or save money) to complex moral questions, some of which would have required them to inflict injury or death on others.

All six subjects with frontal-lobe damage, for example, reported that it would be acceptable to kill one of their own children to save the rest of the family, compared to just half of the control group. For less emotional situations, the presence of brain damage did not have any effect on responses.

The researchers conclude that, for at least some kinds of moral judgments, emotion is a factor in making difficult decisions, rather than a mere aftereffect.