Experimental Listeria meningoencephalitis: macrophage inflammatory protein (MIP)-1a and -2 are produced intrathecally and mediate chemotactic activity in cerebrospinal fluid of infected mice.

In bacterial meningitis, the recruitment of leukocytes across the blood-brain barrier into the central nervous system may be crucial for both elimination of pathogens and tissue injury. In addition to bacterial cell wall products, host factors including chemokines may lead to accumulation of phagocytes within the central nervous system. As shown by Northern analysis, brains of mice infected intracerebrally with Listeria monocytogenes (LM) express mRNA for three chemokines, the macrophage inflammatory protein (MIP)-1 alpha, MIP-1 beta, and MIP-2. The cellular sources of these chemokines comprise both the blood-derived polymorphonuclear leukocytes (PMNs) and monocytes infiltrating the meninges, the ventricular system and the periventricular area. In the course of meningitis a time-dependent increase of MIP-1 alpha and MIP-2 was found in the cerebrospinal fluid (CSF) by ELISA. CSF taken 24 h after infection (CSF-LM24) induced migration of human leukocytes when treated in chemotactic chambers in vitro. Neutralizing Abs to chemokines identified MIP-1 alpha and MIP-2 to be responsible for CSF-LM24 mediated chemotaxis of monocytes and PMNs, respectively. CSF obtained from mock-infected animals contained no MIP-1 alpha or MIP-2 and did not lead to migration of leukocytes. When testing CSF-LM24 on mouse spleen cells, the chemotactic activity detected for mononuclear cells was only partly inhibited by Abs to MIP-1 alpha and -1 beta. Thus, in addition to MIP-1 and -2 other not yet defined chemotactic factors are of importance for recruitment of leukocytes in bacterial meningitis.