Enhanced uptake of multiple sclerosis-derived myelin by THP-1 macrophages and primary human microglia.

BACKGROUND: The pathological hallmark of multiple sclerosis (MS) is myelin phagocytosis. It remains unclear why microglia and macrophages demyelinate axons in MS, but previously found or yet-unknown changes in the myelin of MS patients could contribute to this process. We therefore studied whether myelin from normal-appearing white matter (NAWM) of MS donors is phagocytosed more efficiently than myelin from control donors. METHODS: Myelin was isolated from 11 MS and 12 control brain donors and labeled with the pH-sensitive fluorescent dye pHrodo to quantify uptake in lysosomes. Phagocytosis by differentiated THP-1 macrophages and by primary human microglia was quantified with flow cytometry. Whereas myelin uptake by THP-1 macrophages reached a plateau after approximately 24 hours, uptake by primary human microglia showed an almost linear increase over a 72-hour period. Data were statistically analyzed with the Mann-Whitney U test. RESULTS: MS-derived myelin was phagocytosed more efficiently by THP-1 macrophages after 6-hour incubation (P = 0.001 for the percentage of myelin-phagocytosing cells and P = 0.0005 for total myelin uptake) and after 24-hour incubation (P = 0.0006 and P = 0.0001, respectively), and by microglia after 24-hour incubation (P = 0.0106 for total myelin uptake). This enhanced uptake was not due to differences in the oxidation status of the myelin. Interestingly, myelin phagocytosis correlated negatively with the age of myelin donors, whereas the age of microglia donors showed a positive trend with myelin phagocytosis. CONCLUSIONS: Myelin isolated from normal-appearing white matter of MS donors was phagocytosed more efficiently than was myelin isolated from control brain donors by both THP-1 macrophages and primary human microglia. These data indicate that changes in MS myelin might precede phagocyte activation and subsequent demyelination in MS. Identifying these myelin changes responsible for enhancing phagocytic ability could be an interesting therapeutic target to prevent or inhibit formation or expansion of MS lesions. Moreover, during aging, microglia enhance their phagocytic capacity for myelin phagocytosis, but myelin reduces its susceptibility for uptake.

The use of a test battery assessing affective behavior in rats: order effects.

Many studies have used test batteries for the evaluation of affective behavior in rodents. This has the advantage that treatment effects can be examined on different aspects of the affective domain. However, the behavior in one test may affect the behavior in following test. The present study examined possible order effects in rats that were tested in three different tests: Open Field (OF), Zero Maze (ZM) and Forced Swim Test (FST). The data of the present study indicated that the behavior in ZM was the least affected by the order of testing. In contrast, the behavior in the FST (and to a less extend the OF) was dependent on the order of the test in the test battery. Repeated testing in the same test did not change the behavior in the ZM. However, the behavior in the OF and FST changed with repeated testing. The present study indicates that the performance of rats in a test can be dependent on the order in a test battery. Consequently, these data caution the interpretation of treatment effects in studies in which test batteries are used.