Immunologic Correlates of MS Pathologic Subtypes

Chemokines constitute a family of structurally related polypeptides (MacKay 2001). The chemokines and their receptors exert well-characterized roles in inflammation and physiological function of the immune system, by modulating biological responses, including migration, enzyme secretion, cellular adhesion, cytotoxicity, tumor cell growth, degranulation, and T-cell activation (MacKay 2001; Asensio and Campbell 1999; Gerard and Rollins 2001). Chemokines act through plasma membrane Gprotein coupled chemokine receptors on cellular targets (Luster 1998; Rollins 1997). Chemokines and their receptors have been implicated in various pathologies of the human central nervous system (CNS) and have emerged as salient targets for therapeutic intervention (Asensio and Campbell 1999; Glabinski and Ransohoff 1999; Mennicken et al. 1999; Trebst and Ransohoff 2001). The current study addressed the expression of CC chemokine receptors (CC-CKR) on mononuclear phagocytes in multiple sclerosis (MS). Two variables were imposed on this characterization. First, we evaluated CC-CKRs on mononuclear phagocytes in various stages of lesion evolution. Acute MS lesions (less than 1 month old) exhibit three major zones of demyelinating activity. In the inactive (IA) lesion core, myelin has been completely removed and myelin debris in macrophages is limited to neutral lipid (Lucchinetti et al. 1996). At the expanding lesion edge, in early-active (EA) zones, intracellular myelin debris includes detectable protein (including low-abundance components such as myelin oligodendroglial glycoprotein (MOG) and myelin-associated glycoprotein (MAG; Lucchinetti et al. 1996). Macrophages and monocytes in EA zones express acuteactivation epitopes such as the MRP-14 isoform of the S100 family. In the intermediate late-active (LA) zone, only the abundant myelin proteins such as myelin proteolipid protein (PLP) are found in the intracellular inclusions of macrophages, which also may be demonstrated to contain the lipid-intercalating dye luxol fast blue (LFB). Based on our prior results, we hypothesized that monocyte recruitment to MS lesions could be analyzed by focusing exclusively on the EA zones (Trebst et al. 2001). The further differentiation and activation of these cells could be monitored by evaluating the LA and IA regions of these acute lesions. Second, we compared mononuclear phagocyte CCCKR expression in lesions exhibiting different pathological patterns, as described by Lucchinetti, Bruck, and Lassmann (Lucchinetti et al. 2000). This categorization protocol has been reported and recently reviewed (Lassmann et al. 2001). Lesion patterns were defined by these investigators, as described in Materials and Methods. EA, LA, and IA zones of demyelination were evaluated in both lesion patterns. We found striking differences and informative similarities in our studies of CCR1 and CCR5 expression in pattern II and pattern III lesions. In EA zones of both pattern II and pattern III lesions, infiltrating monocytes (located in perivascular aggregates and expressing MRP-14) expressed CCR1 and CCR5 in the majority of cells. This observation was consistent with our previous report, which was confined to pattern II lesions (Trebst et al. 2001). Taken in the context of data from experimental studies using CCR1or CCR5-deficient mice, these data support a role for CCR1, and possibly CCR5, in the accumulation of monocytes in the human CNS (Rottman et al. 2000). Regulation of CCR1 and CCR5 diverged when LA and IA zones of pattern II and pattern III lesions were compared. Specifically, percentages of CD68 cells expressing CCR5 rose from about 30% in EA zones of pattern II lesions to approximately 80% in LA and IA regions. This observation led to the logical conclusion that CCR5 was maintained on infiltrating monocytes and upregulated on resident microglia in the lesional environment of the pattern II pathology. By contrast, CCR5 expression diminished in LA and IA zones of pattern III lesions, from about 35% in EA zones to 25% 30% in the older regions of these lesions. One possible interpretation of this disparity was that interferon, known to upregulate CCR5 (Hariharan et al. 1999), was present at high levels in pattern II but not pattern III lesions. Expression of CCR1 also differed. In pattern II lesions, as noted above, about 20% of infiltrating cells expressed this receptor, but CCR1-immunoreactive cells were scarce (5% 15%) in LA and IA regions. This finding was interpreted to indicate activation-related downregulation of CCR1 and could be recapitulated in vitro by adherence of monocytes to serum-coated tissue culture flasks (Trebst et al. 2001). By contrast, CCR1 was IMMUNOLOGIC CORRELATES OF MS PATHOLOGIC SUBTYPES