pathway immune response pathway true PW:0000023 https://www.ncbi.nlm.nih.gov/pubmed/27346214 immune response pathway The Immune response pathways mediate the defense of host cells against infection and injury. The first line of defense is provided by the phylogenetically older innate immune response. The later, more versatile response is provided by the pathways of adaptive immunity: the B cell mediated humoral and the T cell mediated cellular or cell-mediated responses.