Four reasons to consider a novel class of innate immune molecules in the oral epithelium

An expanding number of innate immune molecules occupy the "epithelial frontier". This review introduces a recently recognized class of mammalian proteins with similarity to PLUNC ((p) under bar alate, (l) under bar ung and (n) under bar asal epithelium (c) under bar lone), which is itself related to the host defense protein BPI ((b) under bar actericidal/(p) under bar ermeability-(i) under bar ncreasing protein). Four emerging lines of evidence unite the PLUNC-like proteins: conserved genetic structure, epithelial expression, three-dimensional protein similarity, and a physiological response to injury or inflammation. By analogy to known proteins of the innate immune system, an emerging hypothesis for this family is that they act as sensors of Gram-negative bacteria in the oral cavity, among other areas.