CD4+ as Monocytes cell surface receptors
Macrophages and monocytic cells can express CD4, CD8 or even co-express them. The CD4 and CD8 molecules interact with MHC complexes on neighboring cells, and as you can imagine elicit varying effect in a cell type-dependent manner. 

Plainly enough, Zhen et al. demonstrated that monocytic CD4 ligation to MHC-II molecules on other cells, such as activated endothelium, induced an expression pattern conducive to macrophage differentiation (1). Gibbings et al. also demonstrated that CD8 associates with FcyR on the monocyte's surface similar to CD8/TCR associations, and stimulates the secretion of cytokines (2).

I'll try to find a model source, but CD8a on dendritic cells can associate with MHC-II molecules on T cells like HLA-DR and aid in cross-priming the T cells. 

Now what CD4 does on functional, differentiated macrophages is less clear to me, and I need to review the literature on that a bit more. It could just be expression imprinted because they're monocyte-derived cells, or it could also elicit an effect like CD8/FcryR above. I do not know. 

There are more cases, so these serve as selected examples.