TLR2 and rosacea: The Toll-like receptor signaling pathway is a classical innate immune pathway, and TLR2-mediated upregulation of kallikrein-5 activity in macrophages is important for the development of rosacea, as it leads to an increase in the cleavage of antimicrobial peptides and the formation of LL-37, a 37-amino acid peptide that promotes inflammation in the skin.[45,46] In addition to natural immunity, acquired immunity is also involved in rosacea development.