BB:N ESIINTYMINEN ESIM. AIVOISSA

[Bb]

Lähettäjä: Soijuv Lähetetty: 5.1.2005 16:45

Seuraavasta osoitteesta löytyy hyvä tutkimus (koko artikkeli). Tutkimuksen mukaan huomiota herättävä oire neuroborrelioosissa on aivokalvontulehdus.


Infection and Immunity, May 2001, p. 3389-3397, Vol. 69, No. 5
http://iai.asm.org/cgi/content/full/69/5/3389

Discussion: Switching between serotypes provides relapsing fever borrelias with a strategy not only to avoid the host's antibody response but also to exploit different microenvironments, including the brain. For further insight into the mechanism responsible for brain infection by Borrelia spp., we compared the localization of two serotypes of B. turicatae in the brain and other tissues of scid mice. For this, we examined coronal sections of whole-decalcified heads by immunohistochemistry and used H&E-stained sections to compare the inflammatory response to the infection. The major findings were the following: (i) the localization of spirochetes in the brain and spinal cord was primarily leptomeningeal; (ii) there were significantly more serotype A than serotype B cells in the leptomeninges 18 and 40 days after inoculation; (iii) there were significantly more serotype B than serotype A cells in the skin 18 but not 40 days after inoculation; (iv) The tissue with the most severe inflammation was the skin; (v) the dura mater was the first tissue where spirochetes were observed outside of the vasculature; and (vi) the predominant surface lipoproteins VspA and VspB and the periplasmic protein flagellin were expressed at all times in all tissues examined.

Prior studies using cultured brains had demonstrated that serotype A but not serotype B was present in the brain of scid mice 4, 8, and 11 days after inoculation (14). The present study extends this observation to 18 days after inoculation. The localization of serotype A cells in the brain primarily to the leptomeninges was expected. Meningitis is a prominent clinical manifestation of neuroborreliosis in tick-borne relapsing fever and Lyme disease (9, 29). The presence of relapsing fever spirochetes in the brain of experimental animals was known as early as 1922 (7). We knew from our own studies of infection of irradiated mice with B. hermsii that spirochetes cross the blood-brain barrier and are not merely present in the intravascular space of the brain (10). Using nonspecific silver impregnation techniques, the pioneers in the field observed relapsing fever borrelias in the gray matter between neurons and glias (7) and within cerebral capillaries, leptomeningeal vessels, and choroid plexus (24). Relapsing fever borrelias from Africa were observed more commonly in the medulla and deeper parts of the brain than in the cortex of mice and rats (38, 40). The localization was extracellular (20). We were surprised by the small number of spirochetes found in the brain parenchyma compared with the leptomeninges (21). It is possible that examination of brains infected for longer periods of time will reveal increasing localization of borrelias to the brain parenchyma. We confirmed that all spirochetes found in tissues from serotype A- or B-infected mice expressed VspA or VspB, respectively. In a prior study, we showed that VspB is expressed by spirochetes in the blood, joints, and heart of mice (33). Expression of flagellin in infected tissues has been demonstrated in the nonhuman primate model of Lyme disease (11). Down regulation of major surface proteins during infection, known to occur with B. burgdorferi (11, 16), was not observed in these studies.

The localization of spirochetes in the brain has been studied in other spirochetal diseases. In the nonhuman primate model of Lyme disease, spirochetes were found in the leptomeninges, nerve roots, dorsal root ganglia, endoneurium, and extracellular matrix of peripheral nerves, skeletal muscle, heart, and bladder in immunosuppressed animals (11). In contrast, no spirochetes were found in tissues from immunocompetent animals, even those positive by PCR-ELISA (11, 36). B. burgdorferi has been reported intracellularly in vitro in human umbilical vein endothelial cells (22) and macrophages (26) but not in vivo (11). In neurosyphilis, Treponema pallidum was found in the cortex of 25 to 40% of paretic brains examined at autopsy, mainly in the frontal areas, and is difficult to find after treatment (12). In untreated syphilitic lesions in the skin, the majority of treponemes are extracellular (42).

Our studies suggest that borrelias first enter the central nervous system in the subarachnoid space and localize mainly to the leptomeninges, with only a few moving to the brain parenchyma early on. There are two possible routes to reach the subarachnoid space from the circulation: crossing the microvessels of the leptomeninges, and crossing the dura mater-arachnoidal barrier. In support of the first route is the frequent observation of spirochetes located partially in the microvascular lumen and partially in the subarachnoid space of the scid mice. In support of the second route is the observation that the dura mater is the first tissue where spirochetes were found outside of the vasculature. The reason why serotype A cells move into the subarachnoid space significantly better than serotype B cells is unknown. One possibility could be differences in the hydrophobicity of their Vsps: VspA has higher hydrophobicity than VspB (13), and VspB has a more basic pI (33). Another possibility is differences in their binding to glycosaminoglycans or other components of the extracellular matrix. A recent study found that serotype B cells bound to glycoaminoglycans significantly better than serotype A cells, and recombinant VspB but not VspA bound heparin and dermatan sulfate (23). Other bacteria have been found to have variable proteins associated with brain infection. These include the outer membrane protein A of Escherichia coli (25, 35), internalin B of Listeria monocytogenes (31), and the pili and class 5 outer membrane proteins of Neisseria meningitidis (27).

The high number of spirochetes in the skin indicates this tissue favors the multiplication and dissemination of spirochetes. A skin lesion, erythema migrans, characterizes early Lyme disease (6). There is no evidence that B. burgdorferi produces collagenase, elastase, hyaluronidase, or other enzymes that digest extracellular matrix components. However, both B. burgdorferi and the relapsing fever borrelias have been shown to bind human plasmin, plasminogen, and urokinase-type plasminogen activator (15, 19). The binding of plasminogen allows the formation of a bioactive extracellular matrix protease, which facilitates their dissemination through the extracellular matrix of infected tissues (18 ).

We found only mild inflammation in the meninges of the brain and spinal cord of infected animals. Early in the infection of rats with B. turicatae, there was severe congestion of leptomeningeal vessels and parenchymal capillaries, foci of cortical hemorrhages, and intense microglia reaction in the cerebral and cerebellar cortex and hippocampus (24). Later in the infection, there was only lymphocytic infiltration of the leptomeninges. Guinea pigs infected with B. persica had perivascular hemorrhage and infiltration with lymphocytes and macrophages in the brain (1). Selective damage to neurons in the upper part of the spinal cord and posterior columns was found in rats infected with relapsing fever strains from Russia (8 ). Leptomeningeal inflammation was observed only rarely in the nonhuman primate of Lyme disease (11, 30). Two recent studies of mice infected with B. crocidurae (39) and with a relapsing fever Borrelia from Spain (17, 18 ) showed meningitis and brain parenchymal microgliosis. B. crocidurae but not the relapsing fever Borrelia from Spain were observed in the brain parenchyma.

Starting with syphilis and relapsing fever and continuing with Lyme disease, spirochetes remain as important neurological pathogens. A better understanding of the mechanisms by which they cause neurological disease is needed. Our studies suggest that the proteins present in the surface of the spirochetes provide a mechanism for differential localization in tissue during infection. Future studies may elucidate the mechanisms by which spirochetes enter and persist in the brain and cause neurological disease.