Distinctive distribution of lymphocytes in unruptured and previously untreated brain arteriovenous malformation

Abstract

Aim: To test the hypothesis that lymphocyte infiltration in brain arteriovenous malformation (bAVM) is not associated with iron deposition (indicator of microhemorrhage).

Methods: Sections of unruptured, previously untreated bAVM specimens (n=19) were stained immunohistochemically for T-lymphocytes (CD3⁺), B-lymphocytes (CD20⁺), plasma cells (CD138⁺) and macrophages (CD68⁺). Iron deposition was assessed by hematoxylin and eosin and Prussian blue stains. Superficial temporal arteries (STA) were used as control.

Results: Both T lymphocytes and macrophages were present in unruptured, previously untreated bAVM specimens, whereas few B cells and plasma cells were detected. Iron deposition was detected in 8 specimens (42%; 95% confidence interval =20-67%). The samples with iron deposition tended to have more macrophages than those without (666±313 vs 478±174 cells/mm²; P=0.11). T-cells were clustered on the luminal side of the endothelial surface, on the vessel-wall, and in the perivascular regions. There was no correlation between T lymphocyte load and iron deposition (P=0.88). No macrophages and lymphocytes were detected in STA controls.

Conclusions: T-lymphocytes were present in bAVM specimens. Unlike macrophages, the load and location of T-lymphocytes were not associated with iron deposition, suggesting the possibility of an independent cell-mediated immunological mechanism in bAVM pathogenesis.

Keywords: B-lymphocyte; T-lymphocyte; human brain arteriovenous malformation; inflammatory cells; microhemorrhage.

Figure 1

Hemosiderin deposition in unruptured bAVMs. H&E staining (A, B, C) and Prussian blue staining (D, E, F) on the adjacent sections. B & C are enlarged pictures of the regions in squares b & c in A showing hemosiderin positive areas. Insert in B shows two hemosiderin-laden macrophages. D. Prussian blue staining of an adjacent section of A. E & F are enlarged images of the regions in squares e & f in D. Scale bars for A and D: 500µm; for B, C, E and F: 50µm.

Figure 2

CD3⁺ T-lymphocytes and CD68⁺ macrophages. A, B and C. Sections from 3 individual bAVM specimens. C. Sections from an STA. Squares in H&E-stained images are enlarged to show CD68, CD3 and CD20 positive cells in the images next to them. T-lymphocytes and macrophages were detected on the vessel wall (a2 & a3) and between vessels (b2, c2, b3 and c3). Only a few CD20⁺ B-lymphocytes were detected in the lumen (b4) and between vessels (c4). No T- and B-lymphocyte, and macrophage were detected on the wall of STA. Scale bar for a1-d1: 500µm; scale bar for a2-a4: 100µm; scale bar for b2-b4, c2-c4, d2-d4: 20µm.

Figure 3

Location of CD3⁺ T-lymphocytes. T-lymphocytes were distributed in the perivascular region (A), in the vessel wall (B), and on the surface of the endothelial lining (C). Scale bar: 50µm.

Figure 4

Quantification of inflammatory cells in bAVM. (A) Bar graph shows a trend towards more CD68⁺ cells in hemosiderin-positive (HS⁺) bAVMs than in hemosiderin-negative samples (HS⁻). (B) Bar graph shows that the numbers of CD3⁺ T cells were similar in hemosiderin-positive (HS⁺) and negative (HS⁻) samples.