Abstract
The aim of this study was to determine expression, not previously described, of PLUNC (palate, lung, and nasal epithelium clone) (BPI-fold containing) proteins in major and minor salivary glands from very early fetal tissue to the end of the second trimester and thus gain further insight into the function of these proteins. Early fetal heads, and major and minor salivary glands were collected retrospectively and glands were classified according to morphodifferentiation stage. Expression of BPI-fold containing proteins was localized through immunohistochemistry. BPIFA2, the major BPI-fold containing protein in adult salivary glands, was detected only in the laryngeal pharynx; the lack of staining in salivary glands suggested salivary expression is either very late in development or is only in adult tissues. Early expression of BPIFA1 was seen in the trachea and nasal cavity with salivary gland expression only seen in late morphodifferentiation stages. BPIFB1 was seen in early neural tissue and at later stages in submandibular and sublingual glands. BPIFA1 is significantly expressed in early fetal oral tissue but BPIFB1 has extremely limited expression and the major salivary BPIF protein (BPIFA2) is not produced in fetal development. Further studies, with more sensitive techniques, will confirm the expression pattern and enable a better understanding of embryonic BPIF protein function.
Highlights
The bactericidal permeability increasing protein (BPI)-fold (BPIF) containing/Plunc family of putative innate defence genes is located in a single locus on human chromosome 20q11.2, and members of the family are predominantly expressed in regions of the oral cavity, nasopharynx and upper respiratory tract.[1]
BPI-fold (BPIF) Containing/plunc protein expression in human fetal major and minor salivary glands across the PLUNC/BPI family suggested that PLUNC proteins might function by binding lipid molecules and this led to the hypothesis that PLUNCs may share host defence functions with BPI and LPS-binding protein (LBP).[6,7,8]
Expression of BPIFA2 and BPIFB1 was extremely limited with BPIFA2 only being detected in the laryngeal pharynx (Figure 3) and BPIFB1 being seen in small areas of the developing brain
Summary
The BPI-fold (BPIF) containing/Plunc (palate, lung, and nasal epithelium clone) family of putative innate defence genes is located in a single locus on human chromosome 20q11.2, and members of the family are predominantly expressed in regions of the oral cavity, nasopharynx and upper respiratory tract.[1] Protein expression of the prototypic family member, BPIFA1/Plunc, (palate, lung and nasal epithelium clone) was first described in the nasal epithelium of the mouse embryo and the trachea/bronchi of adult mice.[2] An extended family of proteins was subsequently identified, and these are known to make up the largest branch of a lipid transfer protein family that includes phospholipid transfer protein (PLTP), cholesterol ester transfer protein (CETP), bactericidal permeability increasing protein (BPI) and LPS-binding protein (LBP).[3,4,5] The considerable structural similarity. BPIFA proteins have structural homology to the N-terminal domain of BPI whereas BPIFB proteins have structural homology to both domains of BPI.[4,7]
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