If the two antibodies are directly conjugated to dye, you can definitely use them together. If you are using indirect detection with fluorescent secondaries, you can still use mono and poly as long as the primaries are from different species, and as long as the secondaries are cross absorbed and recognise only the intended species.
Alternatively, you can perform sequential staining with a heat retrieval or stripping procedure between the first and second staining. For immunofluorescence you can apply the Opal system.Article Leucocyte dynamics during the evolution of human coronary at...