  An analysis of the couplings of the 210 dimensional SO(10) vector multiplet
to matter is given. Specifically we give an $SU(5)\times U(1)$ decomposition of
the vector couplings $\bar{16}_{\pm}-16_{\pm}-210$, where $16_{\pm}$ is the
semispinor of SO(10) chirality ${\pm}$, using a recently derived basic theorem.
The analysis is carried out using the Wess-Zumino gauge. However, we also
consider the more general situation where all components of the vector
multiplet enter in the couplings with the chiral fields. Here elimination of
the auxiliary fields leads to a sigma model type nonlinear Lagrangian.
Interactions of the type analysed here may find applications in effective
theories with the 210 vector arising as a condensate. The analysis presented
here completes the explicit computation of all lowest order couplings involving
the $16_{\pm}$ of spinors with Higgs and vectors multiplets using the basic
theorem.
