Development of immunoassays for serum tartrate-resistant acid phosphatase isoform 5a.
BACKGROUND
Serum tartrate-resistant acid phosphatase (TRACP) consists of 2 structurally related isoforms, TRACP 5a and 5b. TRACP 5b is from bone-resorbing osteoclasts. TRACP 5a may be a macrophage product of inflammation. We used a novel antibody to TRACP 5a to standardize immunoassays for serum TRACP 5a activity and protein.


METHODS
Biotinylated anti-TRACP antibodies were used to immobilize serum TRACP isoforms. TRACP activity was measured using 4-nitrophenyl phosphate as substrate. TRACP 5a protein was measured with an independent peroxidase-conjugated anti-TRACP antibody. Immunoassays were standardized for linearity of serum dose response, sensitivity and precision. Reference ranges for TRACP 5a were established from serum of 50 healthy males and 50 healthy age-matched females. Serum TRACP 5a activity and protein were determined in 29 cases of rheumatoid arthritis.


RESULTS
Serum matrix interference in both TRACP 5a assays required dilution to 10% serum to approach linearity. Intra-assay and inter-assay CV% were <10%. Mean serum TRACP 5a activity and protein were significantly higher in healthy men than women. There was a slight, but significant age related increase in both serum TRACP 5a and 5b among females, but not males, from age 20 to 70 years. TRACP 5a activity was positively correlated to TRACP 5a protein in healthy sera. Neither TRACP 5a activity nor protein was correlated strongly to TRACP-5b activity. TRACP 5a protein was significantly increased in 8/29 RA sera, whereas TRACP 5a and 5b activities were not. TRACP 5a activity and protein were not significantly correlated in RA sera.


CONCLUSIONS
Although TRACP 5a and 5b are related biosynthetically, their circulating levels in healthy humans were independent, suggesting differential regulation of expression. In chronic diseases, increased TRACP 5a may represent pathological processes of inflammation unrelated to bone metabolism.
Chao
Tsu-Yi
TY
Division of Hematology and Oncology, Tri-Service General Hospital, National Defense Medical Center, Taipei, Taiwan.
Lee
Su-Huei
SH
Chen
Mary M
MM
Neustadt
David H
DH
Chaudhry
Uzma A
UA
Yam
Lung T
LT
Janckila
Anthony J
AJ
D000135:Acid Phosphatase / Q000097:blood* / Q000276:immunology; D000328:Adult; D000368:Aged; D001172:Arthritis, Rheumatoid / Q000097:blood; D005260:Female; D006801:Humans; D007118:Immunoassay / Q000379:methods*; D007527:Isoenzymes / Q000097:blood* / Q000276:immunology; D008297:Male; D008875:Middle Aged; D000071681:Tartrate-Resistant Acid Phosphatase
D007527:Isoenzymes; C000605510:ACP5 protein, human; D000135:Acid Phosphatase; D000071681:Tartrate-Resistant Acid Phosphatase