Figure 1.

Innate immune cell responses to bacillus Calmette–Guérin (BCG) vaccination. The initial immune response to BCG occurs at the site of inoculation (usually the dermal layer of the skin) where resident macrophages and dendritic cells (DCs) interact with the bacillus via different receptors expressed on their surface. Macrophages and DCs phagocytose the bacteria initiating the innate immune response through the secretion of immunomodulatory components such as cytokines and chemokines. Bacteria are degraded via intracellular killing mechanisms and their peptides are trafficked to the plasma membrane along with major histocompatibility complex (MHC) class I and II where they are presented to cells of the adaptive immune system. Neutrophils also enter the site of inoculation and participate in the response. Finally, DCs, loaded with bacteria, and expressing antigen on their surface, home to draining lymph nodes. Abbreviations: P–L, phagosome–lysosome; ROS, reactive oxygen species; RNS, reactive nitrogen species; CRs, complement receptors; TLR, toll-like receptors; GPCRs, G-protein-coupled receptors; CLRs, C-type lectin receptors; MR, mannose receptor; MINCLE, macrophage inducible Ca²⁺-dependent lectin; NLRs, NOD-like receptors; FcγRs, Fcγ receptors; SRs, scavenger receptors; DLNs, draining lymph nodes; DC-SIGN, dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin.