Anti Rnp In Serum

Introduction

Highly purified SM/ RNP antigen complex is purified from calf thymus, bound to microwells & stabilized for extended shelf life. Diluted patient sera are placed in the microwells & incubated. If anti- RNP (or anti-Sm) antibodies are present, they will bind to the antigen in the microwell. The microwells are then washed to remove residual sample & a second incubation with anti-human IgG conjugated to alkaline phosphatase is carried out. The conjugate will bind immunologically to the anti-SM and/or anti- RNP IgG of the antigen-antibody complex, forming a 'sandwich' consisting of:
Conjugate (Enzyme-labeled Anti-human IgG)
Human anti-SM and/or anti- RNP ( IgG)
Well Coated with SM/ RNP antigen
Unbound conjugate is removed in the subsequent washing step. Enzyme substrate is then added to the microwell & if bound conjugate is present, the colorless substrate (p-nitrophenyl phosphate), will be hydrolyzed to form a yellow end product, ( p-nitrophenol). The reaction is then stopped and the color fixed. The intensity of the color is measured photometrically at 405 nm & is proportional to the concentration of anti-SM and/or anti- RNP present in the patient sample. The anti-Sm antibody value in EU/ mL is then subtracted from the test EU/ mL to give the anti- RNP value.

Antibodies to RNP are detected at high frequency (up to 46%) in patients with systemic lupus erythematosus ( SLE) either alone or in parallel with Sm antigen. The RNP antigen is very closely associated with the Sm antigen. However, in contrast to anti-Sm, anti- RNP is found in patients with a variety of connective tissue diseases, including scleroderma, rheumatoid arthritis, discoid lupus & Sjogren's syndrome. A very high titer of anti- RNP, in the absence of other antibodies, is highly characteristic of mixed connective tissue disease ( MCTD).
SLE patients who produce RNP antibodies in the absence of anti-Sm antibodies have a low frequency of nephritis & antibodies to DNA whereas patients who produce both RNP & Sm have a higher frequency of nephritis & anti-DNA antibodies. The comparative data on anti-Sm & anti- RNP presence/absence & levels can thus have diagnostic significance.

Serum is separated from the clot & refrigerated, 2-8 degrees C for short term storage or stored frozen, -20 degrees C, for long term storage. Avoid freeze-thaw cycles. CAUTION: Serum samples should not be heat inactivated, as this may cause false positive results.

Henry, John Bernard, Clinical Diagnosis amd Management by Laboratory Methods, W. B. Saunders Co., Philadelphia, 1991. pp 891-892.
The Physicians Guide to Anti-DNA Antibody Testing, Diamedix Corporation, Miami, Aug. 1989. pp 1-6.
Summary of Procedure. DiaMedix Corporation, Miami, June 1991. pp 1-8.
Medical Knowledge Self Assessment Program (MKSAP) 14, American College of Physicians, Philadelphia 2006

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