Lymphokine-activated killer (LAK) and adherent LAK (A-LAK) activity in multiple sclerosis

NK cell-mediated lysis of autologous human oligodendrocytes

Although considered an autoimmune disease, the mechanisms underlying oligodendrocyte (OL)/myelin injury in multiple sclerosis (MS) remain to be established. We utilized in vitro assays to demonstrate that human OLs, as well as other glial elements (astrocytes, microglia), were susceptible to injury mediated by peripheral blood-derived mononuclear cell preparations (MNCs) enriched for natural killer (NK cells) by depleting CD3(+) +/- CD19(+) cells through use of either magnetic beads or cell sorting. Cytotoxic effects of the NK cell-enriched effectors were dependent on pre-exposure of these cells to IL-2. Furthermore, we found that autologous OLs were as susceptible to injury mediated by IL-2 activated NK cells as were heterologous OLs. In context of the tissue injury that occurs in MS, our results suggest that the inflammatory milieu in MS lesions could provide conditions required for NK cell activation and that such effector cells can bypass the putative protective effects of self-MHC class I molecules that may be expressed on OLs.

A role for natural killer cells in the immunopathogenesis of multiple sclerosis

Seventeen relapsing-remitting (R/R) multiple sclerosis (MS) patients and age/sex matched controls were studied every 6 weeks for 2 years. Disease activity, determined both clinically and by serial MRI, was correlated with natural killer (NK) cell functional activity (FA) and phenotype. Mean NK cell FA is significantly lower in MS patients, compared to controls (P < 0.001), while variability around the means is significantly greater (P < 0.01). The spectrum of mean NK cell FA, observed in the patient cohort, along with cyclical nature of the FA and phenotype over time, observed in both patients and controls, may begin to explain the discrepant results reported in previous studies. In R/R MS, there is a significant correlation between reductions (valleys) in NK cell FA and the development of active lesions on MRI, new (P < 0.001) or enlarging (P = 0.05). More importantly, a significant number of active lesions, new (P = 0.01) and enlarging (P = 0.02), are preceded by a reduction in NK cell FA. The correlation between the onset of clinical attacks and valleys of NK cell FA is also significant (P = 0.002). When taken together, the results suggest that reductions (valleys) in NK cell FA represent periods of susceptibility for the development of active lesions on MRI and clinical attacks. A significant positive correlation is also identified between mean NK cell FA for each R/R MS patient and total number of active MRI lesions developed by that patient over the 2 years (P = 0.001). The results would suggest that R/R MS patients with a higher mean NK cell FA are at greater risk for the development of active lesions. These results support the proposal that NK cells may play a role in the immunopathogenesis of R/R MS.

Non-MHC-Restricted Cell-Mediated Lysis of Human Oligodendrocytes In Vitro: Relation with CD56 Expression

Oligodendrocytes and their myelin membranes are the apparent target of the autoimmune response that characterizes the human adult central nervous system-demyelinating disease multiple sclerosis. Human oligodendrocytes do not express MHC class II molecules, a requirement for MHC-restricted injury mediated by myelin-reactive CD4+ T cells, the cell type implicated in initiating the disease process. In this study we observed that human adult central nervous system-derived oligodendrocytes can be susceptible to non-MHC-restricted lysis mediated by myelin basic protein-reactive CD4+ T cell lines. Cytotoxicity was significantly greater (37 ± 4 vs 7 ± 3%) with cell lines in which a high proportion of cells (mean, 28 ± 6%) expressed CD56 compared with cytotoxicity mediated by low CD56 cell lines (8 ± 2%). High CD56 cell lines, when rested in IL-2, lost cytotoxic activity and had reduced expression of CD56 (mean, 5 ± 2%). CD4+ T cells isolated from short term (3-day) anti-CD3/IL-2-activated mononuclear cell cultures did not express CD56 and were not cytotoxic to oligodendrocytes unless lectin was added. In contrast, an enriched population of non-T cells extracted from the same activated MNC cultures expressed CD56 as well as other NK cell-associated surface molecules and was cytotoxic. These results indicate the potential susceptibility of human oligodendrocytes to non-MHC-restricted injury mediated by both Ag-reactive and nonspecific cellular immune effector cells, with CD56 expression being a common feature of the effector cells.

Increased perforin expression in multiple sclerosis patients during exacerbation of disease in peripheral blood lymphocytes

The expression of perforin (P) in subpopulations of the PBL of multiple sclerosis (MS) patients in stable and active phase of disease was investigated, by simultaneous detection of P (intracellular molecule) and cell surface antigens. A significant increase of CD4+P+ (p < 0.02) and CD16+P+ (p < 0.001), and decrease of CD56+P+ (p < 0.05) cells in active MS was found. In active disease there is a highly significant increase (p < 0.001) of average fluorescence intensity (AFI) for P in CD4(dim+) cells, and these cells are larger in size and have higher granularity (p < 0.05) compared to CD4(bright+) p(dim+) cells. Surprisingly, there were no CD25+P+ cells in either group of MS patients. These results show that CD4+P+ cells are upregulated in active disease in cell number, in the level of P expression per cell, and in the level of cell activation (increase in cell size and granularity). It is suggested that CD4+P+ cytotoxic cells may play a role in the pathogenetic mechanisms of MS.