  We construct a class of superprocesses by taking the high density limit of a
sequence of interacting-branching particle systems. The spatial motion of the
superprocess is determined by a system of interacting diffusions, the branching
density is given by an arbitrary bounded non-negative Borel function, and the
superprocess is characterized by a martingale problem as a diffusion process
with state space $M(\IR)$, improving and extending considerably the
construction of Wang (1997, 1998). It is then proved in a special case that a
suitable rescaled process of the superprocess converges to the usual super
Brownian motion. An extension to measure-valued branching catalysts is also
discussed.
