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BPI fold containing family A, member 4 (BPIFA4) is a non-human protein encoded by the Bpifa4 gene in monkey and cow. It is also known as Latherin in horse, encoded by the Lath/Bpifa4 gene but somewhat divergent from the other species. Latherin/BPIFA4 is a secreted protein found in saliva and sweat.

In humans no protein is normally expressed and BPIFB5P is present only as a pseudogene BPIFB5P. However, it has appeared as a secreted product in breast cancer cell lines, previously named BASE (breast cancer and salivary gland expression) protein.

Superfamily
BPIFA3 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.

Function
In humans, the expression of the BPIFA4P pseudogene into functional BPIFA4 protein is unclear. Although identified as a pseudogene not capable of coding for a protein, the RNA sequence for a putative protein has been detected at moderate levels in several glands (including salivary and mammillary), skin, and breast cancer. This is consistent with the expression of normal BPIFA4/Latherin found in saliva and sweat of other species such as cow, horse, The function of BPIFA4 in those species is associated with BPIFA gene family members' properties of being a surfactant and binding to bacterial lipopolysaccharides. Sweat helps animals cool down, and in animals with pelts (fur) BPIFA4/Latherin significantly reduces surface tension of sweat, acting as a wetting agent to facilitate evaporative cooling. Further, it is speculated that the presence of a surfactant protein in the saliva of ruminant animals (e.g., cow, horse, sheep) may assist in mastication of large quantities of vegetable matter in their diet. BPIFA4 in saliva also may function as a first line of defense against bacteria, via bactericidal functions similar to other BIPFA and BIPFB family members.