TNF and bacterial infectious disease: In the retina, resident microglia can recognize microbial pathogen-associated molecular pattern (PAMP) molecules via Toll-like receptors (TLRs), and upregulate the secretion of proinflammatory cytokines, including interleukin (IL)-6, IL-1β, and tumor necrosis factor-α (TNF-α), as well as major histocompatibility complex (MHC) II, an essential element for antigen presentation to T cells during peripheral bacterial infection (51, 52).