  We prove that if $\mathcal{L} \subset \mathbb{R}^n$ is a lattice such that
$\det(\mathcal{L}') \geq 1$ for all sublattices $\mathcal{L}' \subseteq
\mathcal{L}$, then
  \[
  \sum_{\substack{\mathbf{y}\in\mathcal{L}\\\mathbf{y}\neq\mathbf0}}
(\|\mathbf{y}\|^2+q)^{-s} \leq \sum_{\substack{\mathbf{z} \in
\mathbb{Z}^n\\\mathbf{z}\neq\mathbf{0}}} (\|\mathbf{z}\|^2+q)^{-s}
  \] for all $s > n/2$ and all $0 \leq q \leq (2s-n)/(n+2)$, with equality if
and only if $\mathcal{L}$ is isomorphic to $\mathbb{Z}^n$.
