Nature Immunology pp 920 - 927

Staphylococcus aureus is an important human pathogen that can hide from the immune system. In the September issue of Nature Immunology, scientists have identified a staphylococcal protein that can block the complement cascade – an important arm of the early immune response – aiding the bacteria to escape detection by the immune system.

Rooijakkers and colleagues show that SCIN, a protein secreted by S. aureus, inhibits a key molecule in the complement pathway called C3 convertase. By binding to C3 convertase, SCIN effectively switches off the complement cascade, reducing the ability of immune cells to engulf and kill S. aureus. This molecule could prove useful for the treatment of complement-related diseases in the future.

Nature Immunology pp 881 - 888

Immune cells such as lymphocytes constantly traverse throughout the body in search of infection. Two reports in the September issue of Nature Immunology suggest exit of immune cells from peripheral tissues does not passively occur but requires the expression of a specialized receptor called CCR7.

Earlier work revealed lymphocytes exit the bloodstream to percolate through the tissues, such as the lung or skin, and then return to the bloodstream via an indirect route. These traveling cells re-enter the blood through lymphatic vessels that channel cells and excess fluids towards regional lymph nodes. Cells can then exit lymph nodes to re-enter blood. This process was thought to occur passively by hydrodynamic pressure differences between tissues and lymph fluid.

Now, Butcher and colleagues show lymphocyte tissue exit is not random. They noticed increased numbers of T lymphocytes that expressed the chemokine receptor CCR7 in lymph fluid, whereas cells that did not express CCR7 were retained in the tissues. This finding suggested some selective process was at work. Lymphocytes from CCR7 mutant mice failed to enter lymphatic vessels and instead accumulated in tissues. Independently, Luster and colleagues also found CCR7 was required for lymphocyte exit from lungs in a mouse model of asthma. Accordingly, CCR7 is the ticket for lymphocytes making their way out of tissues. Immune modulators that communicate through CCR7 could therefore potentially be used to alter the course of local inflammatory reactions where lymphocytes accumulate.

Nature Immunology pp 857 - 860

The genetic modification of plants provides a necessary solution for feeding the ever-increasing world population. However, manipulating the genetic makeup of plants may inadvertently result in the production of new proteins that can cause allergy. In a Commentary in this month's Nature Immunology, Dean Metcalfe discusses the steps taken to detect such new food allergens from genetically modified plants and also discusses the limitations of these safeguard measures.

Because we still do not have a precise understanding of what makes certain food items allergenic, it is important to take appropriate steps to detect potential new allergens. In 1996, the relevant governing agencies across the globe proposed a set of guidelines for testing for food allergens from genetically modified plants. This set of guidelines was revised in 2001. As Metcalfe points out however, at present individual evaluations such as testing on animals or looking for similarity to proteins that might be allergenic are not fail-safe. Although these assessments will improve with advances in the underlying scientific understanding of allergy induction, Metcalfe reinforces the idea that the best way forward is a combination of many analyses.