The following is a summary of “Expression and regulation of Siglec-6 (CD327) on human mast cells and basophils,” published in the January 2023 issue of Allergy & Immunology by Smiljkovic, et al.

The effector cells of allergic responses, mast cells (MC), and basophils, exhibit a variety of activation-linked cell surface antigens. However, only a small number of these antigens are functionally significant and selectively expressed in these cells. For a study, researchers looked for surface chemicals that were unique to MCs and basophils, as well as their cellular organization and control during cytokine-induced and IgE-dependent activation.

In order to identify surface antigens and evaluate how antigen expression varies in response to activation, multicolor flow cytometry was used.

They discovered that human MC and basophils have Siglec-6 (CD327) as a surface antigen that is differently regulated. In individuals with mastocytosis and in reactive states, Siglec-6 was abundantly expressed on MC in the bone marrow, but it was not found on other myeloid cells, with the exception of basophils and monocytes. Siglec-6 was found on a fraction of CD19+ B lymphocytes, a few CD14+ monocytes, and CD203c+ blood basophils in healthy people, allergy patients, and patients with chronic myeloid leukemia (CML), but not on other blood leukocytes. Siglec-6 expression was more pronounced in CML basophils compared to normal basophils. Siglec-6 was expressed more on normal and CML basophils when IL-3 was present, and more on tissue MC when stem cell factor was present. Unexpectedly, in IL-3-primed basophils, IgE-dependent activation caused Siglec-6 to be downregulated, but in MC, IgE-dependent activation enhanced stem cell factor’s ability to cause Siglec-6 to be upregulated.

A dynamically controlled marker of MC and basophils is siglec-6. Siglec-6 responded differently in activated MC and basophils, including cytokine-dependent upregulation and distinct, cell-specific responses to IgE-receptor cross-linking.