[85] Whether the corresponding LTo stromal subsets are present in these TLOs is not entirely clear. The importance Nivolumab cost of SLO stromal cells in microbial defence is well documented. During inflammation, FRCs up-regulate anti-microbial genes[24] and the disruption of stromal networks (via viral infection) leaves the host susceptible to secondary infection,[43] an immunodeficiency

that is reversed by the restoration of stromal architecture via LT expression by LTis.[89] Whether specific stromal populations in TLOs versus SLOs have a differential capacity to induce an antimicrobial state is not known. However, viral infection models hint at a major role for TLOs in the defence against pathogens. Well-developed inducible Tyrosine Kinase Inhibitor Library bronchial-associated lymphoid tissue (iBALT) is a form of TLO formed during acute influenza infection,[90] via stromal chemokine expression[91] in a process that is stabilized by myeloid cells.[92] Other processes, including the expression of IL-17 by T cells, appear to contribute to iBALT generation in some experimental contexts,[93] however, the absolute requirement for this cytokine in iBALT generation is unclear.[94, 95] Interestingly mice that lack SLOs, but retain iBALT, can withstand higher inoculations of virus[90] and have a fully intact memory CD8+ T-cell compartment in the context of influenza infection.[96] Hence TLOs can assume

a host-protective role in some infectious contexts by providing a microenvironment that supports the local generation of a protective immune response. Further support for a role of TLOs in a protective response to infectious Celecoxib insult, comes from evidence that antigen persistence in itself is important for the maintenance of TLO structure during chronic infection. So the eradication of

Helicobacter pylori antigen via antibiotics leads to drastic mucosa-associated lymphoid tissue regression,[57] presumably because the TLO has performed its function. Although it is clear that TLO formation can help to increase the efficiency of antigen presentation to lymphocytes for a protective immune response, TLOs can also initiate immune responses that may be responsible for inducing or exacerbating an autoimmune response. Although there is no definitive causal link between TLO presence and disease, in certain autoimmune diseases such as multiple sclerosis (or the murine model experimental autoimmune encephalomyelitis), TLO presence correlates with increased disease severity.[97, 98] TLOs in the pancreas skew B cells toward an autoreactive phenotype during diabetes[99] and a recently described model of murine salivary gland pathology is characterized by TLO formation, ectopic stromal chemokine expression and GL7+ germinal centre development that initiates autoimmunity by breaking self-tolerance to antigen.