Researchers may have discovered a second molecular 'switch' that turns off the immune system's response against HIV. Last year the same team identified a molecule that suppresses the activity of HIV-specific CD8 T cells that should destroy virus-infected cells. Now they describe how a regulatory protein called CTLA-4 inhibits the action of HIV-specific CD4 T cells that control the overall response against the virus.

Tiny pieces of genetic material called microRNA could be key to HIV's ability to evade detection in the immune system. Researchers have shown that when an HIV-infected individual receives a powerful cocktail of antiviral agents called HAART, the virus uses miRNAs to help it hide and remain practically undetectable, temporarily shutting down its ability to replicate. Learning to manipulate miRNA's inhibitory effects might have implications for new strategies against the virus.

As policymakers debate what levels of ozone in the air are safe for humans to breathe, studies in mice are revealing that the inhaled pollutant impairs the body's first line of defense, making it more susceptible to subsequent foreign invaders, such as bacteria.

How do we choose our mates? For quite some time now, scientists suspect that it is not for looks or fashion, neither for love or sympathy. It may be the genes that determine our preference for certain males or females. A new study provides support for this idea by looking at lemurs in Madagascar. Female fat-tailed dwarf lemurs live in life-long pairs, yet notoriously cheat on their partners to improve the genetic fitness of their offspring.

Contrary to arguments by critics, a new study found that legalizing physician-assisted suicide in Oregon and the Netherlands did not result in a disproportionate number of deaths among the elderly, poor, women, minorities, uninsured, minors, chronically ill, less educated or psychiatric patients. Of 10 "vulnerable groups" examined in the study, only AIDS patients used doctor-assisted suicide at elevated rates.

It's a long-standing question: Can just the act of observing an experiment affect the results? According to a new study, if the experiment uses a fluorescent dye called acridine orange, the answer is a resounding "yes." A fluorescent marker, long used in imaging to help researchers watch membrane-bound vesicles as they exit a cell, can actually cause the vesicles to break open as soon as they're hit with light from a microscope. New research describes how to differentiate a microscopy side effect from the cell's true process.

A study of families in the Netherlands indicates that children raised by lesbian couples "do not differ in well being or child adjustment compared with their counterparts in heterosexual-parent families." Among the most interesting findings, lesbian biological mothers were significantly more satisfied with their partners as a co-parent than were heterosexual mothers.