Protein A immunoadsorption in chronic refractory ITP reverses increased platelet activation but fails to achieve sustained clinical benefit.
Adults with chronic relapsing ITP present a difficult therapeutic challenge. The ongoing antibody-mediated platelet destruction in this group might be expected to be associated with increased expression of platelet surface membrane activation antigens. We have studied a group of 10 patients with refractory ITP and 35 healthy controls. Using an immediate, sensitive, unfixed, whole blood, flow cytometric method to detect platelet surface P-selectin and GP53, we have detected markedly increased platelet activation in the ITP group compared with the controls (P-selectin; patient median 24.5% v control median 2.0%. GP53 median 6.5% v 2.1%, P < 0.01 for both). Five patients underwent protein A immunoadsorption therapy. The effect of protein A immunoadsorption on platelet activation before, during and after 18 treatments in these patients was studied and patients were followed-up to assess clinical outcome. Platelet-associated immunoglobulin measurements were made before and at the end of six treatments. Platelet activation decreased after immunoadsorption. P-selectin expression fell significantly; pre- and post-treatment median values differed by 15.5%, P < 0.01, for GP53 the difference was 2.5%, P = NS. A reduction in both platelet-associated IgG (median reduction of 11.8 ng/10(6) platelets, P = 0.08) and IgM (7.6 ng/10(6) platelets, P = 0.06) was recorded.
Cahill
M R
MR
Department of Haematology, Royal London Hospital, Whitechapel.
Macey
M G
MG
Cavenagh
J D
JD
Newland
A C
AC
D000328:Adult; D000368:Aged; D002908:Chronic Disease; D005260:Female; D005434:Flow Cytometry; D006801:Humans; D007163:Immunosorbent Techniques; D008297:Male; D008875:Middle Aged; D019007:P-Selectin / Q000378:metabolism; D015539:Platelet Activation; D016553:Purpura, Thrombocytopenic, Idiopathic / Q000097:blood* / Q000628:therapy; D013205:Staphylococcal Protein A; D017211:Treatment Failure
D019007:P-Selectin; D013205:Staphylococcal Protein A