BPI fold containing family A, member 2 (BPIFA2), also known as Parotid Secretory Protein (PSP), is a protein that in humans is encoded by the BPIFA2 gene. The BPIFA2 gene sequence predicts multiple transcripts (splice variants); 2 mRNA variants have been well characterized. The resulting BPIFA2 is a secreted protein, expressed at very high levels in the parotid (salivary) gland; at high levels in oropharyneal mucosa, including tongue; and at moderate levels many other tissue types and glands including mammary gland, testis, lung, bladder, blood, prostate, adrenal gland, kidney, and pancreas. Superfamily BPIFA2 is a member of a BPI fold protein superfamily defined by the presence of the bactericidal/permeability-increasing protein fold (BPI fold) which is formed by two similar domains in a "boomerang" shape. This superfamily is also known as the BPI/LBP/PLUNC family or the BPI/LPB/CETP family. The BPI fold creates apolar binding pockets that can interact with hydrophobic and amphipathic molecules, such as the acyl carbon chains of lipopolysaccharide found on Gram-negative bacteria, but members of this family may have many other functions. Genes for the BPI/LBP/PLUNC superfamily are found in all vertebrate species, including distant homologs in non-vertebrate species such as insects, mollusks, and roundworms. Within that broad grouping is the BPIF gene family whose members encode the BPI fold structural motif and are found clustered on a single chromosome, e.g., Chromosome 20 in humans, Chromosome 2 in mouse, Chromosome 3 in rat, Chromosome 17 in pig, Chromosome 13 in cow. The BPIF gene family is split into two groupings, BPIFA and BPIFB. In humans, BIPFA consists of 3 protein encoding genes BPIFA1, BPIFA2, BPIFA3, and 1 pseudogene BPIFA4P; while BPIFB consists of 5 protein encoding genes BPIFB1, BPIFB2, BPIFB3, BPIFB4, BPIFB6 and 2 pseudogenes BPIFB5P, BPIFB9P. What appears as pseudogenes in humans may appear as fully functional genes in other species. In humans, the BPIFA2 gene was first identified as a human PLUNC-related gene. It had been identified shortly before as human PSP and nearly a decade and half earlier as the mouse PSP gene. Function The function of PSP had remained unknown for many years until it was finally recognized to be within the BPI/LBP/PLUNC family, and then the bactericidal properties of that family was recognized for BPIFA2/PSP/SPLUNC2. It is primarily secreted into saliva and is therefore among the first line of defense against pathogens entering the mouth. BPIFA1 can bind to lipopolysaccharide (LPS) on bacteria