This is really just a comment on Brendan McKay's answer, but I'd like to point out that there are also infinite self-complementary graphs with minimum degree $\delta=1$. Here are two different ways to see that.
I. From the existence of arbitrarily large finite self-complementary graphs with $\delta=1$ it follows, by the compactness theorem of first-order logic, that there is an infinite self-complementary graph with $\delta=1$. This is because the class of structures $(V,E,f)$, where $(V,E)$ is a graph with $\delta=1$ and $f:V\to V$ is an isomorphism from that graph to its complement, can be characterized by first-order sentences.
II. Start with any self-complementary infinite graph $G$. (For example the random infinite graph or Rado graph is self-complementary; of course every vertex of Rado's graph has infinite degree.) Now you can construct a self-complementary infinite graph with $\delta=1$ by appending to $G$ a $4$-point path, as in Brendan McKay's answer.