Immunohistochemistry (IHC) has become an indispensable tool in cellular immunology, enabling precise visualization and localization of specific proteins within tissue sections. By combining antibody-based detection with advanced imaging techniques, IHC provides critical insights into cellular composition, signaling pathways, and spatial organization within tissues. Recent developments, including multiplexed IHC and high-resolution imaging, allow simultaneous detection of multiple biomarkers at the single-cell level, revealing complex cellular interactions in both health and disease. These approaches are pivotal for understanding immune cell infiltration, activation states, and tissue-specific responses, offering valuable applications in cancer immunotherapy, autoimmune disease research, and infectious disease studies. By linking molecular expression patterns to cellular function, IHC continues to drive innovations in immunology and translational medicine.