Tissue tropism of SARS-CoV-2 variants in ex vivo cultures of human respiratory tract. Immunohistochemical staining of SARS-CoV-2 nucleoprotein in ex vivo cultures of human nasal turbinate at 48 hpi (A), bronchus with infection at 33°C (B), 37°C at 72 hpi (C) and lung tissues at 72 hpi (D) infected with wild-type (WT), Delta and Omicron variants (BA.1, BA.1.1 and BA.2). Positive cells are red-brown. Scale bar, 100 μm. The images are representative of two individual donors.