Plasmocytes are the white blood cells responsible for antibody production. Plasmocytes are found in the bone marrow, lymph nodes and spleen, but not in the blood. The presence of plasmocytes in the blood (ratio generally below 0.10) indicates a higher production of these cells, usually in response to a recent viral, bacterial or parasitic infection that triggered antibody production. A higher plasmocytes ratio (> 0.15) is also found in multiple myeloma, plasma cell leukemia and bone marrow cancers specifically involving plasmocytes. The observation of plasmocytes can be expressed as a ratio (or percentage of white blood cells) in billions per litre of blood (x 109/litre) or in a semi-quantitative manner during visual examination of a smear under a microscope (few, some, several).