We report here on three novel observations: (i) the decrease of serum concentrations of two proteins of the lectin pathway during the acute phase of ischemic stroke; (ii) an inverse correlation of ficolin-3 levels obtained 3-4 days post-admission with the severity and outcome of acute ischemic stroke; (iii) the independent effect of low ficolin-3 and high CRP levels on the outcome of the disease.
As compared to healthy subjects, the serum concentrations of both ficolin-2 and ficolin-3, initiator proteins of the lectin complement pathway, were significantly lower in the samples taken from patients with ischemic stroke immediately after admission (i.e. within hours after the onset of the symptoms). The levels of these proteins did not further change during the initial 3-4 days of stroke. The differences observed between stroke patients and healthy individuals seem to be valid, since the ficolin-2 and ficolin-3 concentrations measured in the sera of healthy subjects are similar to previously reported data . In addition, ficolin-2 and ficolin-3 levels were significantly lower in sera of patients with definite stroke compared to patients with severe carotid atherosclerosis without clinical event as well. The main age of this group was equal to that of stroke patients. This control group of patients exhibited even higher ficolin levels than healthy subjects. These data may suggest that the decreased levels of ficolins in the acute phase of stroke were not related to the chronic and severe atherosclerosis, but rather a decrease in ficolin-2 and ficolin-3 concentrations may happen in the very early phase of the acute ischemic event. In addition, these data indicated that the difference in ficolin concentrations comparing healthy controls and stroke patients were not related to the difference between their ages.,.
The decreased concentration of ficolins could be observed in the very early phase of ischemic stroke and remained unchanged during the next 3-4 days. It seems reasonable to surmise that this decrease was due to consumption through the binding of the molecules to the apoptotic and necrotic cells in the penumbra of the cerebral infarct . Moreover, ficolin-2 and ficolin-3 have also been shown to be involved in the sequestration of dying host cells . The observations made by Wang et al.  are of particular interest, since these authors reported that maternal plasma concentrations of ficolin-3 and ficolin-2 were significantly (p < 0.001) lower in preeclamptic pregnancies than in uncomplicated pregnancies, due to the sequestration of the proteins in placenta. Additionally, they found that both ficolins but particularly ficolin-3 were associated with ischemic placenta tissue.
According to our second observation, lower level of ficolin-3 in the follow-up samples were associated with greater size of the cerebral infarct indicated by higher S100β levels in the sera. Astrocyte-derived S100β concentration is a marker of the degree and the severity of cellular injury in acute ischemic stroke . The examination of S100β protein has been accepted as a good biomarker of the infarct size [26, 42–44]. The concentration of S100β is known to be the highest 72 hours after the onset of stroke .
In addition, ficolin-3 levels inversely correlated with the indirect measure of the severity of ischemic stroke, i.e. with the NIHSS neurological deficit score. Higher NIHSS scores define more severe deficits .
Additionally, a strong negative correlation was found between ficolin-3 concentration and the outcome of the disease measured with modified Rankin scale. This negative correlation indicates that low ficolin-3 levels are associated with an unfavorable prognosis. This association is most probably secondary to the negative correlation between ficolin-3 on the one hand and the severity of ischemic stroke and the infarct size on the other hand, as discussed above. It is well known that both the high baseline NIHSS score and the high serum S100β levels predict poor prognosis of ischemic stroke, which was also found in the present study (Figure 4). The lack of clinical correlates of ficolin-2 could be explained by the observation that ficolin-3 has the highest concentration and the greatest complement-activating capacity among the lectin pathway initiators .
Complement activation is one of the pathological mechanisms contributing to ischemic/reperfusion injury in ischemic stroke [2–4]. The selective ability for complement activation after the binding of ficolin-3 to dying cells may be responsible for the selective clinical correlation with the levels of this protein. Further studies, including simultaneous measurement of ficolin-3 levels and of the generation of complement activation products, are necessary to confirm this assumption.
Our present findings also support previous data [3, 4, 23], which showed that the lectin complement pathway indeed plays an important role in the pathogenesis of acute ischemic stroke; here we show that a ficolin-3-dependent activation of the lectin pathway also contributes to the pathological processes besides the previously suggested MBL-dependent activation.
Third, in accordance with the previous data [46–48] and earlier work from our groups [3, 27], we measured higher CRP levels in the sera of patients obtained at admission as compared to healthy controls, and high CRP levels measured on day 3 were strongly associated with an unfavorable outcome of ischemic stroke. This latter observation is in accordance with the recent findings of Song et al. . According to our present findings, the clinical associations with the low ficolin-3 and high CRP levels measured in the follow up samples are independent, indicating that they reflect two different pathways of inflammation contributing to the pathogenesis of the disease. These findings may have important therapeutic implications. Anti-inflammatory drugs have already been used for the treatment of ischemic stroke with limited success. Since many pharmacological agents, which are able to inhibit pathological complement activation are either approved for therapeutic purposes (such as C1-inhibitor  or eculizimab ) or are under clinical trials , these may be more efficiently used for treatment of ischemic stroke either alone or in combination with anti-inflammatory drugs.
The paper has some limitations. First of all, the number of patients tested is rather low and no late follow-up samples were collected for ficolin measurements. Nevertheless our observations are novel and may initiate a number of studies.