Figure 3. Leukocyte populations in human CSF under normal and pathological conditions. The relative abundance of cells (percentage of total cells) in CSF from patients was summarized from de Graaf et al.,1 Kivisäkk et al.,25 Neuenberg et al.35 and Provencio et al.9 The predominant cells in normal CSF were T cells (49% CD4+, 19% CD8+). Monocytes were the second most abundant leukocyte found in normal CSF (23%) while B cells, granulocytes and dendritic cells were present at low levels. The percentage composition may change in response to various diseases as illustrated (MS, multiple sclerosis; NB, neuroborreliosis; BM, bacterial meningitis; VM, viral meningitis). B cells were increased compared with normal CSF during infections such as NB (14.2% vs. < 1%) and during MS (3.9% vs. < 1%). Because of large increases in lymphocytes and granulocytes in some diseases, monocytes may increase in number but constitute a lower percentage of the total CSF cell population. For example, monocyte numbers increase approximately 500-fold in BM relative to normal CSF but represent only about 3.8% of total CSF cells.