Abstract
Tertiary lymphoid organs (TLO) or ectopic lymphoid follicles are lymphoid aggregates with specialized structures that form under chronic inflammatory processes (1). Their denomination comes from the resemblance these structures bear with secondary lymphoid organs (SLOs), and include the presence of defined B- and T-cell areas, follicular dendritic cells, the promotion of lymphatic development, and the acquisition of high endothelial venule properties by blood vessels (1). TLOs, however, differ from SLOs in that they are not developmentally preprogrammed and appear after exposure to antigen. TLOs have been described in a variety of inflammatory and infectious settings, including influenza (2) and Mycobacterium tuberculosis (3) infections as well as autoimmune conditions such as rheumatoid arthritis (4), multiple sclerosis (5), and systemic lupus erythematosus (6). There is accumulating evidence suggesting that TLOs may be involved in local immune responses that may occur under inflammatory conditions. As such, development of TLOs often correlates with disease aggravation and promotion of autoreactive T- and B-cell activation in autoimmune conditions (1). However, in some infectious diseases, as is the case in tuberculosis (7), their presence may be associated with development of protective immune responses and improved pathogen control.
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