造成血管神經性水腫（angioneurotic edema）最主要的原因為下列何者？
mast cell degranulation
increased tumor necrosis factor-α
decreased ratio of \mathrm{CD4}^{+} to \mathrm{CD8}^{+} T lymphocytes
\mathrm{CD4}^{+}
\mathrm{CD8}^{+}
Langerhans cell rupture
