In this study of Chinese individuals, we found that the NLR and PLR were both significantly higher in patients with psoriasis than in healthy subjects. Our study is consistent with the results of previous studies of smaller patient populations, and we extended the findings to include a comprehensive and systematic evaluation of the association between psoriasis and multiple hematological parameters, including absolute blood cell counts, NLR, and PLR. Furthermore, we also compared these parameters in patients with the four subtypes of psoriasis. Neutrophils produce many inflammatory mediators and cytokines and are involved in a variety of systemic autoimmune diseases [13]. These cells also form so-called “neutrophil extracellular traps,” which are mesh-like arrays of DNA and protein aggregates that facilitate elimination of pathogens while sparing host cells. A previous study has demonstrated that neutrophil extracellular traps are more abundant in skin lesions and peripheral blood of psoriasis patients compared with healthy subjects [14, 15]. Th17 lymphocytes and their related cytokines are also considered to play crucial roles in psoriasis; however, neutrophils and mast cells are the major source of IL-17A in psoriatic skin lesions [16], substantiating the importance of neutrophils in the pathogenesis of psoriasis. Precious study showed that the levels of NLR in the psoriasis patients were higher than that in healthy controls [11, 17]. Polat M demonstrated that PASI scores was positively correlated with NLR values [11]. However, in accordance with our study, Ataseven A and colleagues found no correlation between NLR and PASI score [17]. A study included 316 psoriasis patients showed that elevated NLR was associated with severity of psoriasis (PASI scores) and non-calcified coronary artery burden. After 1 year treatment of biologics, NLR decreased and the degree of NLR decrease was related to the change of non-calcified coronary artery burden [10, 18]. Consistent with this study, another study demonstrated that PASI scores and NLR values of psoriasis patients can be decreased by systemic therapy, including narrow band ultraviolet B, acitretin, cyclosporine, methotrexate, adalimumab, etanercept, and ustekinumab. The degree of PASI scores and NLR values decrease was positively correlated [19]. However, study also found there was no significant difference of NLR and PLR between pre-treatment and after biologics treatment [20]. Therefore, studies also showed that elevated NLR values were positively correlated with increased PASI scores [12]. A meta-analysis included 1067 psoriasis patients and 799 healthy controls found that NLR were significantly higher in psoriasis patients than healthy controls. Furthermore, NLR and PLR values in patients with PASI > 10 was higher than that of patients with PASI < 10. But there were no association between NLR values and PASI scores [7, 21]. These studies indicate that NLR values were elevated in psoriasis patients and decreased after systemic therapy. But the results of relationship between NLR and the severity of psoriasis were inconsistent. Our study demonstrated that the neutrophil counts and NLR were significantly higher in all four psoriasis subtype groups compared with the control group, with the GPP group having the highest NLR. We assumed that reasons for inconsistent research results may include number of cases, disease duration, types of study (for example retrospective study or prospective study), other disease combined, racial and ethnic differences and so on. Overall, these studies suggest that NLR values were correlated with psoriasis, but may not the severity of psoriasis. In conclusion, whether neutrophil counts and NLR can be used as markers to distinguish between the disease subtypes, and the exact contribution of neutrophils to the pathogenesis of psoriasis, remain to be clarified.
Platelets, which are often elevated during infectious and inflammatory diseases [22], store a number of inflammatory cytokines and chemokines that play crucial roles in psoriasis, such as IL-1β and CXCL8 [23,24,25]. The observed increased abundance of platelets in psoriasis patients compared with control subjects is probably a consequence of chronic inflammation. PLR is another proposed indicator of systemic inflammation [26]. Precious study showed that PLR values in the psoriasis patients were higher compared to healthy controls [11, 17]. Furthermore, PLR values can be downregulated after biologics therapy [7, 20]. A meta-analysis also showed that PLR values were significantly higher in psoriasis patients than that in healthy controls [21].
In agreement with previous studies [7, 11], we found that both peripheral blood platelet counts and PLR are significantly higher in patients with each of the four subtypes of psoriasis compared with the control subjects. The PLR was lowest in the PsV group and similar in the GPP, PsE, and PsA groups. Although these data demonstrate that platelet counts and PLR are increased in psoriasis patients, especially in the most severe subtype, the underlying mechanisms are unclear.
Conflicting data have been reported about the relationship between psoriasis and both RBC and Hb. Several studies have reported no significant difference in Hb levels between psoriasis patients and healthy subjects [12, 27], whereas we found that RBC and Hb were both significantly decreased in all of the psoriasis subgroups compared with the control group. The highest values were observed in the PsV group, with the GPP, PsE, and PsA groups having similar Hb levels. A previous study demonstrated that erythrocyte membrane fluidity was lower in psoriasis patients than in healthy subjects. Moreover, psoriasis patients have been shown to have decreased levels of the antioxidant enzymes superoxide dismutase and catalase and, conversely, elevated levels of the oxidative stress marker malondialdehyde, compared with control subjects [28]. Thus, we hypothesize that the reduction in RBC count and Hb level observed in our cohort of psoriasis patients may be related to neutrophil activation and oxidative stress [29].
Earlier studies found that NLR and PLR reflect disease activity in psoriasis patients [7, 12]; however, we failed to detect a positive association between PASI scores and either NLR or PLR. There are at least two explanations for this apparent discrepancy. For example, NLR and PLR may reflect the inflammatory status of psoriasis patients, but not the disease severity. Alternatively, the PASI may not be sufficiently sensitive to disease symptoms, particularly those of mild to moderate severity and those affecting the nails. Moreover, the index does not take into account the disease impact on quality of life and comorbidities, both of which may influence the ratios [30]. Clearly, further studies are needed to clarify the relationship between PASI scores, PLR, and NLR.
Finally, our study may have limitations, including it was conducted in a single tertiary medical center and was a cross-sectional study, PASI scores of some patients were not calculated, both the patients and healthy controls who combined malignancy except hematological malignancies were not excluded. These may lead to the patients were biased to having higher disease severity and could not fully represent the features of psoriasis patients in China.