gms | German Medical Science

Introduction: Basophil granulocytes represent a small leukocyte population (1%) and are known for their role in allergy and helminth infections. Activation of the cells leads to degranulation with release of inflammatory mediators. Interestingly, recent studies indicate that basophils might influence the pathogenesis of autoimmune diseases like SLE. Therefore, we aimed to investigate the function and phenotype of basophils from these patients and compared them with basophils from healthy individuals. A focus was on the expression and functional involvement of immunoglobulin (Fc) receptors, because it was shown that the IgG-receptor CD32B (FcγRIIB) inhibits cellular activation via the IgE-receptor (FcεRIα).

Methods: Leukocytes of 40 SLE patients and 40 healthy volunteers were isolated with Hetasep. The expression of CD63, CD203c, CD62L, FcγRIIA, FcγRIIB, FcεRIα and the binding of IgG and IgE on the cell surface were determined by flow cytometry. The activation of the cells was measured by the basophil activation test (CD63 and CD203c).

Results: The phenotype and function of basophils from SLE patients were compared with basophils from healthy volunteers. Freshly isolated basophils of SLE patients expressed more CD203c and CD62L, indicating a higher activation status in vivo. This was not associated with an elevated expression of the degranulation marker CD63. The FcγRIIB-expression was higher, whereas the FcεRIα-expression was comparable to basophils of healthy subjects. In accordance with this, basophils of SLE patients bound more IgG on their surface. However, this did not lead to an inhibition of their cellular activation. In the basophil activation test, basophils from SLE patients showed a stronger activation after stimulation with fMLP as well as with crosslinking anti-IgE and anti-FcεRIα-antibodies. Serum factors are responsible for this effect, because the activation of basophils from either SLE patients or healthy individuals was higher after incubation in SLE serum as compared to healthy serum.

Conclusion: In conclusion, circulatory basophils of SLE patients have a more activated phenotype and show a higher activation potential in vitro compared to basophils of healthy subjects. Factors in the serum of SLE patients are responsible for the activating effects on basophils. Currently, we investigate which factors are responsible, such as for example IgG-containing immune complexes.