ALPP

ALPP Full Name

alkaline phosphatase, placental

ALPP Introduction

Placental alkaline phosphatase (ALPP), also widely known as PLAP, is a tissue-specific, membrane-bound metalloenzyme encoded by the ALPP gene located on human chromosome 2. As a prominent member of the alkaline phosphatase isoenzyme family, ALPP functions as a homodimer requiring magnesium and zinc ions for its catalytic activity. Physiologically, ALPP is highly expressed in the placenta during pregnancy, where it plays a critical role in fetal development by catalyzing the hydrolysis of phosphate monoesters, thereby facilitating nutrient transport and regulating local phosphate metabolism. Beyond its metabolic functions, emerging evidence highlights its immunomodulatory roles; ALPP is capable of dephosphorylating and neutralizing pro-inflammatory molecules like lipopolysaccharides (LPS), which contributes to maternal-fetal immune tolerance and innate immune regulation.

Figure 1. Illustration showing the postulated evolutionary relationships of the human liver/ bone/kidney, intestinal, placental and placental-like genes. (Source: Sharma U, et al. 2014)

While ALPP is essential during normal gestation, its aberrant ectopic expression in non-pregnant individuals is strongly linked to various pathological conditions, particularly malignancies. Clinically, ALPP serves as a highly reliable diagnostic and prognostic biomarker for germ cell tumors, including testicular seminomas and ovarian dysgerminomas. Furthermore, abnormal ALPP upregulation has been documented in numerous somatic cancers, such as ovarian adenocarcinoma, endometrial carcinoma, and cholangiocarcinoma. In these oncological contexts, elevated ALPP is frequently associated with tumor progression, immune evasion, and poor patient survival. Because of its highly restricted expression in healthy adult tissues and prominent presence on the surface of specific cancer cells, ALPP is now increasingly recognized not only as a valuable tumor marker but also as a promising target for novel antigen-targeting cancer immunotherapies, such as CAR-T cells and antibody-drug conjugates.

Alternate Names for ALPP

ALPP; alkaline phosphatase, placental; ALP; PALP; PLAP; PLAP-1; alkaline phosphatase, placental type; glycerophosphatase; alkaline phosphomonoesterase; placental alkaline phosphatase 1; alkaline phosphatase Regan isozyme;

• Immunohistochemistry Antibodies for Pathology

• 1. Basiri M, et al. Evaluation of Placental Alkaline Phosphatase Expression as A Potential Target of Solid Tumors Immunotherapy by Using Gene and Protein Expression Repositories. Cell J. 2021 Nov;23(6):717-721.
  2. Sharma U, et al. Alkaline phosphatase: an overview. Indian J Clin Biochem. 2014 Jul;29(3):269-78.