An effective immune response requires the engagement of host receptors by pathogen-derived molecules and the stimulation of an appropriate cellular response. Therefore, a crucial factor in our ability to control an infection is the accessibility of our immune cells to the foreign material. Exosomes-which are extracellular vesicles that function in intercellular communication-may play a key role in the dissemination of pathogen-as well as host-derived molecules during infection. In this review, we highlight the composition and function of exosomes and other extracellular vesicles produced during viral, parasitic, fungal and bacterial infections and describe how these vesicles could function to either promote or inhibit host immunity.

Over 2 billion people are infected with M. tuberculosis (M.tb); however, only 5–10% of those infected will develop active disease. Recent data suggest that containment is controlled locally at the level of the granuloma and that granuloma architecture may differ even within a single infected individual. Formation of a granuloma likely requires exposure to mycobacterial components released from infected macrophages but the mechanism of their release is still unclear. We hypothesize that exosomes, which are small membrane vesicles containing mycobacterial components released from infected macrophages, could promote cellular recruitment during granuloma formation. In support of this hypothesis, we found that C57BL/6 mouse-derived bone marrow macrophages treated with exosomes released from M.tb-infected RAW264.7 cells secrete significant levels of chemokines and can induce migration of CFSE-labeled macrophages and splenocytes. Exosomes isolated from the serum of M. bovis BCG infected mice could also stimulate macrophage production of chemokines and cytokines ex vivo but the level and type differed during the course of a 60 day infection. Interestingly, the exosome concentration in serum correlated strongly with mouse bacterial load, suggesting some role in immune regulation. Finally, hollow fiber-based experiments indicated that macrophages treated with exosomes released from Mtb-infected cells could promote macrophage recruitment in vivo. Exosomes injected intranasally could also recruit CD11b+ cells into the lung. Overall, our study suggests that exosomes may play an important role in recruiting and regulating host cells during an M. tuberculosis infection.

Mycobacterium tuberculosis-infected macrophages and dendritic cells are limited in their ability to present antigen to CD4+ T cells suggesting that other mechanism of antigen presentation are driving the robust T cell response observed during an M. tuberculosis infection. These mechanisms could include antigens present in apoptotic bodies, necrotic debris, exosomes or even release of non-vesicular antigen from infected cells. However, there is limited data to support any of these mechanisms as important in driving T cell activation in vivo. In the present study we use Rab27a-deficient mice which show diminished trafficking of mycobacterial components to exosomes as well as M. tuberculosis strains that express recombinant proteins which traffic or fail to traffic to exosomes. We observed that exosomes released during a mouse M. tuberculosis infection contribute significantly to its T cell response. These finding imply that exosomes function to promote T cell immunity during a bacterial infection and are an important source of extracellular antigen.

Voluntee r tourism has been heavily criticise d for its negative conse quence s on destinations and voluntee rs, often the dire ct result of unrealistic demand -led marke ting and lack of conside ration for the environmental and social costs of host communities. While some industry participants have responded through adhe rence to best practice, little information or support is available about how to responsibly market voluntee r tourism . This research uses an online content analysis based on the Inte rnational Voluntourism Guide lines for Commercial Ope rators to unde rstand the use of responsibility as a marke t signalling tool. Five influential web pages of eight organisations are scored across 19 re sponsibility crite ria and compared against the organisation's le gal status, product type and price .We find that responsibility is not used for marke t signalling; prefe re nce is give n to communicating what is easy, and not wha t is important. The status of the organisation is no guarantee of responsible practice, and price and responsibility communications display an inve rse relationship. We conclude voluntee r tourism ope rators are ove rpositioning and communicating responsibility inconsistently, which highlights greenwashing, requiring at least industry-wide codes of practice, and at be st, regulation. This pape r refle cts on its methodological limitations, and on its practical achievements in e ncouraging change within some of the organisations examined. Victoria Smith is a graduate from the MSc Responsible Tourism Management at LeedsMetropolitan University. Dr Xavier Font is Reader at the International Centre for Research in Events, Tourism andHospitality at Leeds Metropolitan University. His research focuses on understanding reasons for pro-sustainability behaviour and market based mechanisms to encourage s ustainable production and consumption. IntroductionVolunteer tourism (VT) is a hybrid concept, bringing together international volunteering and tourism, "the practice of individuals going on a working holiday, volunteering their labour for worthy causes" (Tomazos, 2009a:196). VT is often promoted as a way to experience authenticity within the context of an alternative tourism beneficial to destinations, leading to expectations of a responsible tourism ethos. The purpose is often "aiding or alleviating the material poverty of some groups in society; the restoration of certain specific environments or research into aspects of society or environment" (Wearing, 2007:1) alongside touristic activities. However, as VT grows in popularity, the true value and costs with regard to the triple bottom line are being called into question (Goodwin, 2011;Wearing, 2001).VT organisations have come under criticism for being overly profit-driven, overpromising benefits, harming destinations and creating customer dissatisfaction (Benson and Henderson, 2011;Crossley, 2012;Simpson, 2004;Tomazos and Cooper, 2012). In this issue of this journal, Taplin, Dredge and Scherrer (2014) outline a monitoring and evalua...