The normal cellular elements in cerebrospinal fluids (CSFs) are mononuclear leukocytes, lymphocytes and monocytes. In adults, the prominent cells are lymphocytes. Mononuklear cell reaction is also the most frequent cytological findings in many pathological conditions. Monocytes and granulocytes are responsible for phagocytosis of various agents (such as bacteria, fungi, viruses, dying or tumor cells), while monocytes and lymphocytes interact to produce an effective immune response (cell mediated and humoral immunity).
Round (immunocompetent) cells
Round (immunocompetent) cells are predominant cellular elements found in normal and many pathologic fluids. They can be seen in resting state (lymphocytes) as well as in different morphologic variants as a result of antigen stimulation. The findings of numerous cell types intermediate between lymphocytes and plasma cells support the hypothesis that the CNS is the site in which this transformation takes place.
Monocyte / macrophage cell line
Monocytes, activated monocytes and macrophages function as phagocytes. They ingest and kill microorganisms, dying and dead cells, tumor cells, denatured proteins and antigen-antibody complexes, etc. (the material ingested is more variable than the material ingested by neutrophil granulocytes). The monocytes/macrophage system also plays a major role in initiating and regulating the immune response. These cells are known as antigen-presenting (APS) cells, processing specific antigen for lymphocyte recognition.
By convention, the leukocytes containing large and easily visible granules are usually called granulocytes. All of these granular cells (fully maturated) have segmented nucleus (polymorphonuclear cells). They are further subdivided into neutrophils, eosinophils and basophils (according to the type of staining reaction found in granules). Granulocytes may degranulate and release a large variety of substances with microcidal inflammatory and diverse further effect.
The variations in their number and type in body fluids are mostly accompanied by specific pathologic conditions, such as neutrophilia in bacterial infections or eosinophilia in parasitic infections.
It is generally stated that granulocytes are never seen in normal CSF samples from adults (however, with the use of cytocentrifuge, an occasional neutrophil is found in a small percentage of normal fluids with a normal total cell count).
The cells lining the CSF space include ependymal cells, choroidal plexus cells, a variant of ependymal cells, and the cells or parts of meninges (such as large mesothelial-like arachnoid cover cells).
It has been shown that very little blood is needed to significantly alter the cellular composition of CSF. A bloody fluid may be caused by a pathologic hemorrhage within the CNS, or by a traumatic puncture.
In most cases, the finding of engulfed red blood cell by phagocyte is the first proper sign of pathologic hemorrhage, vs. "artificial" bleeding.
Alien cells such as bone marrow elements or cartilage cells as a contamination caused by the lumbar puncture may also be encountered.
Differentiation of malignant cells is based on common histologic criteria for the diagnosis of tumor cells. In this cell polymorphism, anisocytosis and polychromasia are most pronounced. Numerous cells in mitosis are seen on a slide.