Mast cells are essential for early onset and severe disease in a murine model of multiple sclerosis

Abstract

In addition to their well characterized role in allergic inflammation, recent data confirm that mast cells play a more extensive role in a variety of immune responses. However, their contribution to autoimmune and neurologic disease processes has not been investigated. Experimental allergic encephalomyelitis (EAE) and its human disease counterpart, multiple sclerosis, are considered to be CD4(+) T cell-mediated autoimmune diseases affecting the central nervous system. Several lines of indirect evidence suggest that mast cells could also play a role in the pathogenesis of both the human and murine disease. Using a myelin oligodendrocyte glycoprotein (MOG)-induced model of acute EAE, we show that mast cell-deficient W/W(v) mice exhibit significantly reduced disease incidence, delayed disease onset, and decreased mean clinical scores when compared with their wild-type congenic littermates. No differences were observed in MOG-specific T and B cell responses between the two groups, indicating that a global T or B cell defect is not present in W/W(v) animals. Reconstitution of the mast cell population in W/W(v) mice restores induction of early and severe disease to wild-type levels, suggesting that mast cells are critical for the full manifestation of disease. These data provide a new mechanism for immune destruction in EAE and indicate that mast cells play a broader role in neurologic inflammation.

Figure 1

W/W^v mice show a delay in disease onset and a reduction in disease severity. (A) Clinical scores were assigned daily to wild-type (n = 16) and W/W^v (n = 17) mice, and the mean of each group was reported (P < 0.0001 as determined by paired t test). (B) Graph represents the percent of total animals that demonstrated disease by day 30 after immunization (P < 0.0003). Curve was plotted according to the method of Kaplan-Meier, and significance was calculated by the log-rank test. Results in A and B represent cumulative data from three independent experiments.

Figure 2

Histologic analyses of CNS tissues in WBB6/F₁ ^+/+ mice. After sacrifice of the animals, brains, spinal columns, and other organs were removed and preserved in 10% neutral buffered formalin. Paraffin-embedded tissue sections were stained with Giemsa (A and B) or hematoxylin and eosin (C and D). (A) Mast cell (arrow) located within the thalamic border region of the habenula; ×40. (B) Two mast cells (arrows) located in the habenula. The third ventricle is also noted (V); ×20. Inset, the same two mast cells ×40. (C) Multiple inflammatory infiltrates (arrows) found in spinal cord section of a diseased animal; ×10. (D) Focal inflammatory infiltrate found in the brain parenchyma of a diseased animal; ×40.

Figure 3

Flow cytometric analysis of the in vitro–differentiated BMMC population. Cells double positive for c-kit and FcεRI were considered mast cells. Greater than 96% of the population was positive for both mast cell markers, c-kit (c-kit–PE) and FcεRI (IgE + rat anti–mouse–FITC).

Figure 4

BMMC transplantation reconstitutes mast cell populations in organs of W/W^v mice. BMMCs were injected intravenously into groups of five to seven W/W^v mice. Mice were housed for 10 wk before being subjected to EAE disease induction along with age-matched W/W^v and wild-type controls. After a 30-d disease course, animals were killed, and Giemsa-stained sections were obtained from paraffin-embedded organ samples. (A) Mast cell (arrow) present in the gut of a wild-type F₁ ^+/+ mouse. Arrowhead denotes blood vessel; ×40. (B) Mast cells (arrows) present in the gut of a BMMC-reconstituted W/W^v mouse; ×40.

Figure 5

Reconstitution of W/W^v mice with BMMCs restores EAE disease onset and severity to wild-type levels. (A) Clinical scores were assigned daily to wild-type (n = 10), W/W^v (n = 8), and W/W^v + BMMCs (n = 12) mice, and the mean of each group was reported (P < 0.0001; post-test results comparing W/W^v to wild-type or W/W^v to reconstituted group: P < 0.001). Repeated measures of ANOVA followed by the Bonferroni post-test was used for comparison of the mean clinical scores of the three groups in the reconstitution experiments. (B) Graph represents the percent of total animals who demonstrated disease by day 30 after immunization (P < 0.004). Curve was plotted according to the method of Kaplan-Meier, and significance was calculated by the log-rank test. Results from A and B represent cumulative data from two independent experiments.

Figure 6

Detection of MOG-specific IgG and IgG subclasses. Upon sacrifice, serum was obtained from wild-type (n = 16), W/W^v (n = 16), and BMMC-reconstituted W/W^v (n = 10) mice and analyzed for MOG-specific isotype and IgG subclass levels by ELISA. Results represent cumulative data from four experiments.