Friday, August 6, 2010

autoimmune antibodies - aren't they confusing?

lets talk about 2 types of commonly ordered antibodies for evealuating autoimmune /vasculitic process.

1.Anti nuclear antibodies - as the name implies these are antibodies against nuclear antigens ( to DNA, to histone, to nonhistone proteins,to nucleolar antigens). So they stain in different ways which forms the basis of differentiating them...
Homogeneous or diffuse nuclear staining - SLE, drug induced SLE ( ab to histones)
Rim or peripheral staining - SLE ( ab against ds DNA)
Fine Speckled nuclear pattern - mixed CTD
Coarse Speckled nuclear pattern - scleroderma ( ab to centromere )
Nucleolar - Systemic sclerosis

Since ANA encompasses all these antibodies, it is very sensitive but not specific for diagnosing individual connective tissue disorders. A titre of 1: 160 and above is considered positive. In a patient with related symptoms, then we can go ahead and order specific antibodies (eg. anti-histone, anti smith etc) .Also about 3% - 5% of Caucasians may be positive for ANA and it may reach as high as 10% - 37% in healthy individuals over the age of 65.

2.Anti neutrophil cytoplasmic antibody (ANCA) - again,as the name implies, these are antibodies against cytoplasmic antigens. done to diagnose vasculitic disorders in the right clinical situation.
There are 2 types

c-ANCA - ab against proteinase3 , and it shows a diffuse staining pattern. positive in 80% of Wegners , 40% of Microscopic polyarteritis,10% of Churg-Strauss syndrome

p-ANCA - ab against myeloperoxidase, and it shows a perinuclear staining. positive in 50%microscopic polyangitis, 50% of Churgstrauss, and in sclerosing cholangitis.
atypical p-ANCA -has been evaluated in Ulcerative colitis, as its positive in upto 80% of pts. they are ab against inner side of nuclear membrane. This is different from the typical p-ANCA, and is diagnosed by seeing them (atypical) getting destroyed in formalin while the typical p-ANCA doesnt. also positive in 88% primary scl cholangitis and 81% of AIH. ( WJG 2007)
hope this helps