The Varicella-Autoantibody Syndrome

Varicella (Chicken Pox) was a very common virus that many children from our generation were infected with. Although most of us had to deal with the typical symptoms, some children also developed life threatening blood clots. A very interesting phenomenon that we discussed in our Immunology class was to blame; Cross-reactivity. The varicella virus produced an immune response that cross-reacted with a protein found in blood called Protein S. The purpose of Protein S is similar to that of an anticoagulant. It basically helps regulate clot formation by deactivating pro-coagulant proteins. Three study groups were analyzed to determine the cause of this antibody and why some children were forming life-threatening clots.

The study groups consisted of 52 children without acute varicella virus exposure and 43 patients with varicella (VZV) exposure. The second group was further broken down into 17 children with thromboembolism (blood clots) or purpura fulminans and VZV and 26 with uncomplicated VZV exposure. There were significant differences between the group without VZV exposure and the group with VZV exposure. Those exposed to VZV frequently developed a lupus anticoagulant (measured by dilute Russel Viper Venom Time dRVVT) and several other antibodies to phospholipids regardless of whether they had uncomplicated exposure or if they developed thromboembolism. Although there was no difference between the two groups when it came to antibodies made in the acute phase, the difference came in duration of antibodies and their effect on Protein S. Those that developed a thromboembolism or purpura fulminans had significantly lower Protein S levels and significantly higher levels of antibodies to Proteins S.

The interesting question that I brought from this paper is: what the difference is between these two groups of children? They both are producing a cross-reactive antibody to VZV and Protein S, but only a small portion develop low levels of Protein S and high levels of antibodies which lead to thromboembolism. Could this be a problem with T cell regulation in these patients? If not, what is different with these patients?

Pubmed:
http://www.ncbi.nlm.nih.gov/sites/entrez?otool=uchsclib&term=the%20varicella-autoantibody%20syndrome&cmd=search&db=pubmed