A distinct biomolecular profile identifies monoclonal mast cell disorders in patients with idiopathic anaphylaxis

Abstract

Background: Clonal mast cell disorders are known to occur in a subset of patients with systemic reactions to Hymenoptera stings. This observation has prompted the question of whether clonal mast cell disorders also occur in patients with idiopathic anaphylaxis (IA).

Objective: We sought to determine the prevalence of clonal mast cell disorders among patients with IA, criteria to identify those patients who require a bone marrow biopsy, and whether the pathogenesis of IA involves a hyperresponsive mast cell compartment.

Methods: We prospectively enrolled patients with IA (≥3 episodes/y) who then underwent a medical evaluation that included a serum tryptase determination, allele-specific quantitative PCR (ASqPCR) for the KIT D816V mutation, and a bone marrow examination. Mast cells were cultured from peripheral blood CD34⁺ cells and examined for releasability after FcεRI aggregation.

Results: Clonal mast cell disease was diagnosed in 14% of patients referred with IA. ASqPCR for the KIT D816V mutation was a useful adjunct in helping identify those with systemic mastocytosis but not monoclonal mast cell activation syndrome. A modified overall clonal prediction model was developed by using clinical findings, a serum tryptase determination, and ASqPCR. There was no evidence of a hyperresponsive mast cell phenotype in patients with IA.

Conclusion: Patients with clonal mast cell disease can present as having IA. Distinct clinical and laboratory features can be used to select those patients more likely to have an underlying clonal mast cell disorder (monoclonal mast cell activation syndrome or systemic mastocytosis) and thus candidates for a bone marrow biopsy.

Keywords: Anaphylaxis; KIT; allele-specific quantitative PCR; mast cell activation; mast cells; mastocytosis; monoclonal mast cell activation syndrome; tryptase.

Figure 1. Bone marrow mast cell flow cytometry and immunohistochemistry in patients with IA (A), MMAS (B), ISM (C)

Flow cytometric results show that CD117+ mast cells gain CD25 surface expression in clonal disease, illustrated by no abnormal CD25+ mast cells in IA (A), two populations of mast cells in MMAS (CD25+ and CD25−, B) and abnormal CD25+ mast cells in ISM (C). Bone marrow biopsies showed no mast cell clusters in IA and MMAS with multiple clusters in ISM.

Figure 2. Immunophenotypic mast cell markers expressed by bone marrow mast cells, mast cell growth and degranulation of cultured human mast cells

Mast cell markers, CD63 and CD203c, are compared in non-clonal (HV, IA) and clonal patient populations (MMAS, ISM) (A, B). Patients with ISM demonstrated the highest expression of CD63 and CD203c, which were significantly higher than both non-clonal populations. Non-clonal populations were similar. Mast cell proliferation from CD34 positive progenitor cells produced more mast cells from patients with IA or ISM (C). Degranulation of mast cells through the IgE receptor was similar amongst groups. (D) (A-*p=0.02, ***p<0.0001), (B-*p=0.04, **p=0.002), (C-*p=0.01, ***p=0.0002)

Figure 3. Pre-post event serum tryptase (A, B) and baseline serum tryptase over time (C, D) in non-clonal and clonal mast cell disease

When compared to baseline, both patients with IA (p=0.001) (A) and with clonal disease (MMAS, ISM) (p=0.002) (B) had a significant rise in serum tryptase with an anaphylactic event. However, the average increase was 502 vs 25 ng/ml for clonal vs IA, respectively. In most patients with IA, the baseline serum tryptase remained stable over time (C), while the majority of patients with clonal disease experienced a gradual rise over time (D). IA (Circles), ISM (triangles), MMAS (squares)