Increased Number of B-Cells In the Red Pulp of the Spleen In ITP

Platelets are targeted by autoantibodies and destroyed in the reticuloendothelial system, e.g. the spleen, in patients with chronic immune thrombocytopenia (ITP). However, other pathophysiologic mechanisms such as platelet destruction by cytotoxic T-cells and defective bone marrow production of platelets also contribute to the thrombocytopenia in ITP. Splenectomy normalizes the platelet count in around 70% of chronic ITP patients, however, precious little is known about the spleen micromorphology in this disease. We examined splenic pathology in patients with ITP, focusing on the intrasplenic distribution of lymphocyte subsets.

The paraffin-embedded block containing representative material of the splenic tissue from 29 splenectomized chronic ITP patients (15 females and 14 males, mean age 45±21 (SD) years) and 11 controls, splenectomized because of traumatic splenic rupture (2 females and 9 males, mean age 48±19 (SD) years), was used to produce serial sections with a thickness of 5 μm. These sections were stained with conventional haematoxylin-eosin, and immunostained to identify CD3, CD4, CD8, CD20 and CD68 using the Dako Envision System in a Techmate Horizon Autostainer (Glostrup, Denmark). Using micromorphometry the lymphocyte subsets were enumerated in the red and white pulp of these spleens.

All ITP patients were preoperatively optimized, using corticosteroids and/or IVIg, and the immediate pre-splenectomy platelet count ranged 5–357 × 10⁹/l.

Significantly more T-cells than B-cells were seen in the red pulp, both in ITP and control spleens (p<0.01). Conversely, more B-cells than T-cells were observed in the white pulp. There was no difference in the number of T-cells in the red and white pulp, between ITP patients and controls. However, the number of B-cells was increased in the red pulp of patients with ITP compared with the controls. Furthermore, numerous B-cells and CD8+ (cytotoxic) T-cells were located in the splenic cords, lining the sinusoids in the red pulp, a microenvironment where they readily can interact with the other blood cells, e.g. platelets.

Chronic ITP is associated with an increased number of CD20+ B-cells in the red pulp of the spleen. The red pulp of the spleen also provides a microenvironment where close interaction between platelets, CD3+, CD4+, and CD8+ T-cells and B-cells can take place. Trafficking of regulatory and effector cells into this microenvironment might be a potential therapeutic target.

No relevant conflicts of interest to declare.