How to improve the diagnosis rate of lupus?

*It is only for medical professionals to read for reference.
SLE diagnosis cannot be ruled out even when anti-Sm antibodies are negative? Anti-Sm antibodies (Anti-Sm antibodies) are often seen in the diagnosis of systemic lupus erythematosus (SLE), and they were first named because they were discovered in a lupus patient named Smith in 1966
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Today, let the editor take everyone to approach the anti-Sm antibody to see what is the relationship between it and rheumatism
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The structure of the primary anti-Sm antibody.
When looking at the test sheet, you will probably find that the appearance of anti-Sm antibody is often accompanied by anti-RNP antibody positive.
The reason is related to the structure of the anti-Sm antibody
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To understand the structure of anti-Sm antibodies, you must first mention U1snRNP.
U1snRNP refers to the snRNP complex particles with U1-RNA as the nucleic acid molecule.
Figure 1 is a schematic diagram of the structure of U1snRNP particles.
It can be seen that anti-Sm antibodies and anti-RNP antibodies are its constituent parts.

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The anti-Sm antibody mainly includes 7 proteins (B/B', D1, D2, D3, E, F, G).
The target antigen of the anti-RNP antibody is 68kDa, protein A and protein C in the complex particles.
Protein
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Simply put, Sm and RNP are different antigenic sites in the same molecular complex, so the two often appear together
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Figure 1.
Diagram of the structure of U1snRNP [1] The detection study of the secondary anti-Sm antibody shows that the frequency of anti-Sm antibodies in different ethnic groups is different, and the detection rate is greater in the black population
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In terms of detection methods, the commonly used detection methods for anti-Sm antibodies include convective immunoelectrophoresis, western blotting, and enzyme-linked immunosorbent assay
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Among them, convective immunoelectrophoresis was first used, but it is generally believed that the sensitivity is low and the specificity is high.
Western blotting and enzyme-linked immunosorbent assay make up for the shortcomings of low sensitivity.
Now most hospitals use Western blotting
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It is worth noting that a detection method that detects antibody negative does not completely exclude the presence of rheumatism.
It should be analyzed in conjunction with clinical and other results.
The use of two or more detection methods at the same time can improve the accuracy of the test
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The clinical significance of the third anti-Sm antibody Anti-Sm antibody is negative in normal people, while anti-Sm antibody is highly specific (over 90%) in SLE, which has been included in the American College of Rheumatology/European Alliance Against Rheumatism (ACR/EULAR) Regarding the classification criteria of SLE, the positive anti-Sm antibody is of great significance for the diagnosis of SLE, and since the incidence of anti-Sm antibody in SLE patients is about 10%-30%, the diagnosis of SLE cannot be ruled out when it is negative
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Studies have shown that in terms of system damage, anti-Sm antibodies are related to kidney involvement in SLE patients [2], especially when anti-ds-DNA antibodies and anti-Sm antibodies are positive at the same time, the probability of kidney involvement is significantly increased.
Anti-Sm antibodies When it is positive, the probability of neurological symptoms is greater than that of patients with pure anti-ds-DNA antibody positive [3]
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In addition, there is still controversy on the indication of disease activity.
Some studies believe that anti-Sm antibodies can indicate disease activity, and some studies believe that there is no parallel relationship between anti-Sm antibodies and SLE disease activity
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Anti-Sm antibodies, together with anti-ds-DNA antibodies, are often considered to be involved in the pathogenic process of the disease, and are of great help to the retrospective diagnosis of early and atypical SLE or SLE after treatment
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Anti-Sm antibodies are highly correlated with SLE, so why are anti-Sm antibodies produced? Researchers have found that Epstein-Barr virus (EBV) infection can induce the production of anti-Sm antibodies through molecular simulation mechanisms [1]
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This is similar to other antibody production mechanisms.
Many studies [4] believe that infections, especially viral infections, play an important role in the occurrence and development of autoimmune diseases
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Comparing SLE patients and healthy people, it can be observed that Epstein-Barr virus infection is more common, and Epstein-Barr virus is considered to be the main pathogen of SLE
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4.
Summary In summary, it can be seen that anti-Sm antibodies are highly specific in SLE and are regarded as marker antibodies for SLE.
However, negative anti-Sm antibodies cannot completely rule out the diagnosis of SLE
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Since Sm and RNP are different antigenic sites in the same molecular complex, they are often positive at the same time.
The appearance of anti-Sm antibodies indicates that patients with SLE are more likely to have kidney involvement
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Viral infection plays an important role in the pathogenesis of SLE, and the production of anti-Sm antibodies may be related to EB virus infection
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Reference materials: [1] Migliorini P, Baldini C, Rocchi V, Bombardieri S.
Anti-Sm and anti-RNP antibodies.
Autoimmunity.
2005 Feb;38(1):47-54.
doi:10.
1080/08916930400022715.
PMID:15804705 .
[2]Li Changhong,Wei Qin,Li Kun,Feng Yanguang,Wei Silu.
The value of anti-Sm antibody detection in systemic lupus erythematosus and lupus nephritis[J].
Imaging Research and Medical Applications,2017,1(18):195-197 .
[3]Janwityanuchit S,Verasertniyom O,Vanichapuntu M,Vatanasuk M.
Anti-Sm:its predictive value in systemic lupus erythematosus.
Clin Rheumatol.
1993 Sep;12(3):350-3.
doi:10.
1007/BF02231577.
PMID :8258234.
[4]Getts DR,Chastain EM,Terry RL,Miller SD.
Virus infection,antiviral immunity,and autoimmunity.
Immunol Rev.
2013 Sep;255(1):197-209.
doi:10.
1111/imr.
12091.
PMID: 23947356; PMCID: PMC3971377.