In the presented paper, 60 KD children were included in this retrospective study and divided into 5 groups according to different age interval. There are no obvious differences in the sex distribution in terms of the incidence of KD in all groups. Other studies reported the disease more frequently occured in boys [16, 17]. However, our result has a discrepancy with those results, but is consistent with the data recently reported from Australia [18]. On this issue, a study including a larger number of patients will lead to more convincing conclusion.
Neutrophil recruitment is an early event induced by the bacteria infection except for severe trauma, massive haemorrhage, malignancy and chemical poisoning [19, 20] and lymphocyte loss is usually looked as early biomarkers for systemic spread of severe infection [21]. Our results revealed that in the acute phase of KD, the abnormal elevated neutrophil percentages and the decreased lymphocyte percentages before IVIG are the main characteristics of laboratory parameters for KD children. The simultaneous occurrence and correlation of these two changes suggests that bacterial infection is most likely an inducer of KD. The treatment of IVIG can effectively control the infection-induced inflammatory response and regulate the body's immune function to normal levels. It also suggests the use of antibiotics during the acute phase of KD may contribute to the improvement in KD and have a synergistic effect with IVIG.
As it known, a child’s maturity of immune system will not reach until adolescence. Not until 2 years old, adaptive immunity could not largely approach those of healthy adult levels and full immune competence will not truly reach until the teenage years [22]. Therefore, it is understandable that in our study, the correlation coefficients (r) between the changes from both the neutrophil and the lymphocyte are higher with the rise of age. These results also indicate IVIG has a better immune-modulatory effect on KD patients 4 years old and more, manifesting as a better balance between cellular subgroups such as neutrophil and lymphocyte.
CD19+ B cell is immunoglobulin production cells and plays major role in the humoral immune response. In our study, in KD children’s acute phase, before IVIG, the obviously increased count of CD19+ B cells shows its activation and proliferation under the stimulation of antigen indicating its predominant role in patients’ activated humoral immunity. It has been reported that in mice CD19 enhances the B cell receptor (BCR) induced signaling which is crucial for the activation and proliferation of B cells and the following enhanced response of humoral immune [23, 24]. As to our knowledge, our presenting finding is evidence from patients that proliferating CD19+ B cell plays dominant role in the active humoral immune among KD children 4 years old or older.
What’s more, in our study, the presented linear correlation between the decreased extent of IL-10 and the absolute counts of CD19+ cell suggests that CD19+ B cells may have a function of IL-10 secretion. In the classic immunology theory, IL-10 known firstly as an anti-inflammatory cytokine when study found Th2 cells could secrete it together with other Th2-type cytokines such as IL-4, IL-5. Later, investigators found that other types of cells including macrophages, DCs, mast cells even neutrophils have the secretion function of IL-10 [25]. A study confirmed that B cell when in deficiency of CD19 could not produce higher IL-10 compared with the wild type B cells. In their CD19 -/- mice model, the animal displayed a reduced production of IL-10 by B cells and developed a more serious disease [26]. Another study demonstrated that in mice reactive oxygen species could suppress humoral immune response through the reduction of CD19 expression and resultant BCR signaling [23]. In some patients treated with rituximab, the depletion of B cell leaded to immune disorder [27]. It is also reported that B cells from multiple sclerosis patients secreted markedly less IL-10 than that from healthy donors [28] suggesting the possible IL-10 secretion function of B cells in human. Combined with our results, it is reasonable to speculate that the abnormally high counts of CD19+ B cell may be a result from the overactive humoral immune of KD patients. These proliferating CD19+ B cells have the function of the IL-10 secretion acting as a compensatory response trying to keep balance of immune response to normal level.
After the treatment of IVIG, patients’ IL-10 reduced significantly suggesting the CD19+ cell absolute count may have a tendency of decrease. Considering another phenomenon that the patients’ mean percentage of lymphocyte increased while that of the neutrophil decreased after IVIG, we put forward that there are possible other subtypes of lymphocytes activated to proliferate. As known the functions of immune globin are complex involving modulation of the expression and function of Fc receptors, interference with the activation of complement and the cytokine network, provision of anti-idiotypic antibodies, effector functions of T cells and B cells and so on [29]. Specially, IVIG could bind to the siglecs expressed on the surface of neutrophils and result in the cell death [30]. In addition, IVIG containing Fc has the ability to stimulate the expression of a population of natural regulatory T cells (nTreg) [31]. In our patients, after experiencing IVIG treatment, although the cell count of CD19+ B cell decreased, lymphocyte percentages increased suggesting other major ingredients of lymphocytes, T cells, which also acts as an antigen presentation cell may be actively stimulated to proliferate. Therefore, after therapy of IVIG, the balance of the disordered immune responses tends to recover including the inhibition of excessive active humoral immune and the boost of cellular immune in KD children older than 4 years old, whose immune system are approaching to maturation. In KD children at 4 years and older, the combination of CD19+ B cells absolute count before IVIG treatment with the decrease extent of IL-10 expression after IVIG treatment can be used as potential sensitive indicators for assessing the body's inflammatory response status and evaluating effects of IVIG treatment.
In this study, as to our knowledge, we put forward data of KD children aged 4 years and older for the first time that CD19+ B cell is stimulated to be active and proliferate directing to the enhanced function of humoral immune response, which have verified in mice but have not clearly confirmed in KD patients in previous study. From our point of view, in children with KD, activated proliferating CD19+ B has IL-10 secretion function, and IVIG can inhibit this effect, thereby inhibiting cellular immunity, activating humoral immunity, and regulating immune response. However, more laboratory data need to be collected to confirm further the conclusion.
However, there are still some limitations in this retrospective analysis including the number of cases involved in are not fully enough and the data collected from a single center so that it could not completely reveal the overall perspective epidemiology of KD accurately. Although Xinhua Hospital is not only a comprehensive hospital affiliated to Shanghai Jiao Tong University School of medicine but also contains pediatric medical centre, which is one of four major pediatric hospitals in Shanghai, a city more than 20 million people living in. Children patients affected by KD from Shanghai even part of north China will receive medical treatment here.
Secondly, in the presented study, before and after the treatment of IVIG,the absolute cell count of subsets in lymphocyte especially the number of CD19+ cell should be monitored dynamically in order to observe the trend of lymphocyte subsets more clearly.
Another limitation is that it is impossible to verify the effects of CD19+ B cell function elimination in patients. However, it could tried in mice. At the other hand, it is possible to collect subset of cells to culture in vitro so to study the IL-10 secretion function of CD19+ B cell.
In the following study, we will enroll more KD children aged 4 years and older. During the therapy course of KD children, more detail examinations will perform to study in-depth the mechanism under the relationship between CD19+ B cell count and the expression level of IL-10.