Tuesday, March 31, 2009

How Hot is Your Tea?

photo by prakhar

Researchers at the University of Tehran have found a link between drinking steaming hot tea and an increased risk of esophageal cancer, as published in the British Medical Journal. The study looked at people living in the Golestan province of Iran, an area where individuals drink over a liter of tea a day. Esophageal cancer has several contributing factors, including heavy alcohol consumption, tobacco use, chronic acid reflux, diet and obesity. Although alcohol and tobacco are the main contributors in the US and Europe, these activities are not common in Golestan, yet this province has one of the highest rates of esophageal cancer in the world.

By studying the tea drinking habits of individuals with esophageal cancer compared with healthy participants in the region, it was determined that drinking tea at a temperature of 70C or higher increased the risk of esophageal cancer 8-fold compared to drinking tea at a temperature of 65C or less. So does this mean you should have a thermometer handy every time you want a soothing cup of tea? Not necessarily, but if anything, it is probably a good idea to avoid drinking scalding hot tea or liquids in general. Further investigations into how heat can lead to the development of cancer as well as the prevalence of medical conditions within the Golestan population that could lead to esophageal cancer susceptibility will continue to shed light on this interesting observation.

Sources: BBC News- Steaming Hot Tea Linked to Cancer;
NHS News- Hot Tea and Cancer

Tuesday, March 24, 2009

The Not So Sweet Smell of DEET

photo by rob lee

Those darn mosquitoes! If you’ve ever gone camping or hiking, you have most likely used N,N-Diethyl-meta-toluamide, commonly known as the insect repellent DEET. So how does DEET manage to keep pesky bugs away? In the case of mosquitoes, it appears that they smell DEET directly. The hair-like sensory organs found on the antennae and maxillary palps of mosquitoes house olfactory receptor neurons (ORN) which sense smell. With increasing concentrations of DEET, increased neuronal excitation occurs within the ORNs, indicating that the act of smelling is causing a reaction and the response is dose-dependent.

Mosquitoes not only smell DEET directly, they also avoid it. When Petri dishes were set containing either solvent or DEET-treated filter paper, mosquitoes landed in the solvent-only area significantly more. Likewise, when mosquitoes were given the option to fly towards sugar-treated cotton only after passing through an area where DEET vapors were being released, they avoided landing or departed shortly after landing. This further indicates that an interaction between mosquitoes with actual odorants is not necessary for DEET-induced repellency-- the mosquitoes are able to smell DEET and avoid it.

Reference: Syed Z and Leal WS. (2008) Mosquitoes smell and avoid the insect repellent DEET. PNAS. 105(36):13195-6.

Wednesday, March 18, 2009

Dendritic Cells to the Rescue

photo by burning image

Dendritic cells (DCs) are immune cells in the body which collect antigens in tissues, process the antigen, and then present the antigen to other immune cells, such as T cells, mounting an immune response. Put more simply, DCs are always on the look out for those bad guys that invade our bodies, like viruses. Once DCs capture these pathogens, they transport them to other cells which can fight against the invader.

Several types of DCs exist, including ones that lie in the dermis (layer of skin below the epidermis), termed “dermal dendritic cells” (DDCs). Upon visualizing the behavior of DDCs under normal conditions, they appear to be highly motile and actively crawl through spaces within the dermis. To see how DDCs would react upon introduction of a pathogen, researchers injected skin with the protozoan parasite Leishmania. This parasite is transmitted by sand flies which bite individuals, depositing the parasite into the dermis, causing cutaneous leishmaniasis. When DDCs encountered the parasite, their behavior and morphology changed rapidly- they became stationary and extended long, motile pseudopods capable of reaching out to and engulfing the pathogens. In fact, multiple parasites were incorporated into small compartments within the DDC. This shows how DDCs quickly respond to “danger signals”, allowing for the initiation of an immune response. So thank your DCs for slowing down every now and then and taking care of your unwelcome guests!

Reference: Ng LG, Hsu A, Mandell MA, Roediger B, Hoeller C, et al. (2008) Migratory dermal dendritic cells act as rapid sensors of protozoan parasites. PLoS Pathog 4(11): e1000222. doi:10.1371/ journal.ppat.100022 2

Monday, March 16, 2009

HIV: The Wolf in Sheep’s Clothing

photo by sarahheiman

"I can’t live if living is without you”…these may be words sung and spoken by many, but if a virus could speak, these are the exact words it would say to the cell it infects. Viruses, such as HIV, act like parasites and use the proteins and replication machinery present in the host cells they infect in order to propagate themselves. When viruses replicate and bud out of the cells they infect (T cells in the case of HIV), they take along some of the cell’s proteins and incorporate them into their own viral envelope. Uninfected T cells also normally release small particles called microvesicles which are involved in modulating immune responses. When such microvesicles bud out of T cells, they take with them proteins from the T cell plasma membrane.

A recent study has examined the carbohydrate composition of proteins coating the surface of HIV derived from infected T cells to that of microvesicles derived from uninfected T cells. The study shows that the carbohydrates present on virions were the same as those found on native microvesicles, indicating that HIV can cleverly camouflage itself within the host by covering itself with a “coat” that closely mimics immunomodulatory microvesicles.

Reference: Krishnamoorthy L, Bess JW Jr, Preston AB, Nagashima K, Mahal LK. (2009) HIV-1 and microvesicles from T cells share a common glycome, arguing for a common origin. Nature Chemical Biology 5(4):244-50.