Pleocytosis is a term used to describe an increased cell count {Gk. pleion more}, usually referring to an increase in white blood cell

White blood cell

White blood cells, or leukocytes , are cells of the immune system involved in defending the body against both infectious disease and foreign materials. Five different and diverse types of leukocytes exist, but they are all produced and derived from a multipotent cell in the bone marrow known as a...

 (WBC) count in a bodily fluid, such as cerebrospinal fluid

Cerebrospinal fluid

Cerebrospinal fluid , Liquor cerebrospinalis, is a clear, colorless, bodily fluid, that occupies the subarachnoid space and the ventricular system around and inside the brain and spinal cord...

 (CSF). It is often defined specifically as an increased WBC count in CSF.

It is indicative of an inflammatory

Inflammation

Inflammation is part of the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the organism to remove the injurious stimuli and to initiate the healing process...

, infectious

Infection

An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...

, or malignant

Malignant

Malignancy is the tendency of a medical condition, especially tumors, to become progressively worse and to potentially result in death. Malignancy in cancers is characterized by anaplasia, invasiveness, and metastasis...

 condition. CSF pleocytosis in patients suspected of having Guillain-Barre' Syndrome (acute demyelinating polyradiculoneuropathy) should prompt consideration of other diagnoses, such as HIV, CMV, West nile virus infection (in appropriate setting, Lyme disease (neuroborreliose), or other infectious or inflammatory conditions.

Increased white blood cell count in the blood is rather termed leukocytosis

Leukocytosis

Leukocytosis is a raised white blood cell count above the normal range in the blood. It is frequently a sign of an inflammatory response, most commonly the result of infection, and is observed in certain parasitic infections...

.