Role of multiple sclerosis treatment on neutrophil multifaceted functions against bacteria.

Background: According to some authors, disease-modifying treatment (DMT) in multiple sclerosis (MS) may increase infection risk. As revealed in our previous research work, supported by an ESCMID Research Grant, an impairment of polymorphonuclear cell (PMN) intracellular killing activity was detected in treated MS patients suggesting that this defect might well play a key role in increasing infection risk, which has been associated with an increased risk of developing MS and its exacerbations. On this ground, the aim of this study was to evaluate the direct role of most common immunosuppressive or immunomodulatory agents, of MS therapy, on the functions of healthy subject (HS) neutrophils subjected to an in vitro drug pretreatment, and to correlate these results with those obtained on PMNs by treated MS patients. Material/methods: The functional activity of HS-PMNs pre-treated with either immunosuppressive (i.e. natalizumab, fingolimod) or immunomodulatory (i.e. interferon beta 1β, glatiramer acetate) drugs, at the concentration achieved in vivo, was assayed. To achieve this purpose PMN-intracellular killing activity towards Klebsiella pneumoniae, the cytokine release profile, the apoptosis, the reactive oxygen species (ROS) production and surface molecule expression (CD11b, CD62L, CD66b, TLR2 and TLR4) were evaluated. The same parameters were assessed by testing PMNs from 60 MS patients (16 untreated, 25 treated with immunomodulatory and 19 treated with immunosuppressive drugs). Statistical analysis was performed using the Graphpad Prism version 6.00 P-values inferior to 0.05 were considered significant. Results: Drug pre-treated HS-PMNs showed a reduction in bacterial intracellular killing with statistically significantly lower values (p<0.05), than those registered for non pre-treated controls during the different incubation times (Figure 1). In the same experimental conditions, no variations in the cytokine release, apoptosis, ROS production and surface molecule expression of the HS-PMNs were observed under both stimulated and unstimulated conditions. With regard to MS patients, out of all these assessed parameters, the only variation registered in PMNs from treated MS patients was a noticeable reduction in bacterial killing (p<0.05). Conclusions: As microbe killing is a critical physiological function of PMNs, involving various mechanisms and although apoptosis, ROS, cytokine and surface molecule production do not seem to have an impact on the differences observed in the defective killing capacity of treated-MS PMNs, other mechanisms might be involved. Hence, we can deduce that the PMN impairment detected in the treated MS patients, strongly linked to the treatment itself, may contribute to increased exacerbations and microbial infection onset. In this regard, a deeper understanding of the priming condition exerted by treatments in neutrophils from MS patients could be a clue for the complete comprehension of MS pathogenesis.