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Letters to the Editor
Figure 2. Cytokine serum levels in patients with autoimmune hemolytic anemia and relationship with hematologic parameters and endogenous erythropoietin levels. Upper panel: serum cytokine individual val- ues of autoimmune hemolytic anemia (AIHA) patients before therapy with recombinant erythropoietin (rEPO). Grey areas indicate mean+1 standard deviation of 40 age and sex matched healthy controls. TNF-α level was lower in AIHA than in controls (P<0.001), whereas IL10, IL6, IL17, and TGF-β levels were all higher (P<0.001, P<0.001, P=0.014, and P=0.002, respectively); IFN-γ level was comparable between patients and controls. Cytokines were evaluated using commercialeEnzyme-linked immunosorbent assay kits. Lower panel: correlation between endogenous EPO, bone marrow reticulocytes index (BMRI), hemoglobin (Hb) and cytokines. TNF-α positively correlated with endogenous EPO (r=0.77, P=0.005), and negatively with BMRI (r=-0.052, P=0.05). Moreover, IL6 and IL17 positively correlated with BMRI (r=0.45, not significant; r=0.53, P=0.04, respectively). Similar correlations were observed for reticulocytes (TNF-α: r=-0.051, P=0.05; IL6: r=0.53, P=0.04; IL17: r=0.61, P=0.02). Finally, a neg- ative correlation was observed between TGF- β and Hb values (r=-0.63, P=0.04). Dashed line: negative correlation; continuous line: positive correlation.
For the first time, we showed that EPO levels were inappropriately low compared to hemoglobin levels in the majority of patients. Even if reduced, endogenous EPO maintained a negative correlation with Hb values, reticulocyte counts and bone marrow responsiveness index. As expected, patients who were transfused showed lower levels of endogenous EPO, possibly indi- cating that the feed-back loop (anemia- hypoxia – EPO production) is intact in AIHA. Interestingly, patients with AIHA showed significantly reduced EPO values com- pared to other types of anemia. These findings are similar to what has been described for immune thrombocytope- nia, where low or inappropriately normal levels of endogenous thrombopoietin have been demonstrated12 and have led the way to TPO-receptor agonists use. The question is why AIHA patients show reduced EPO levels compared to other anemias. It may be speculated that reticulocyte response to hemolysis, by reversing the rela- tive hypoxia (of the anemic state), may give a negative feed-back to the kidney. This may result in inhibition of EPO production, similar to what has been observed in transfused patients. Another possible mechanism may be due to the quick instauration of anemia in AIHA where massive erythrocyte destruction may occur in a few
hours, whilst bone marrow compensation requires more time.1-4 Finally, the existence of a “stunned bone marrow” unable to build up a prompt response to anemia as observed in patients with septic state13 may be hypothe- sized. In this setting, a temporary EPO stimulation may be preferred to additional immunosuppression.
In a fraction of cases, serum levels of TNF-α, inter- leukin 10 (IL10), IL6, IL17, TGF-β, and IFN-α were eval- uated (Figure 2) and showed a different pattern in patients versus matched controls. As already reported, a shift towards T-helper 2 (Th2) and T-helper 17 pheno- type was observed, with reduced TNF-α and increased levels of IL6, IL10, TGF-β, and IL17, consistently with a prevalent humoral autoimmune response. Despite the limited number of cases and the known variability of cytokine levels, we found interesting correlations with endogenous erythropoietin levels. In particular, TNF-α, a known negative regulator of erythropoiesis, positively correlated with EPO levels and negatively with reticulo- cyte response. The Th2 cytokines IL6 and IL17 were pos- itively related to reticulocytosis mirroring the degree of autoimmune attack. Finally, TGF-β has a negative impact on Hb levels, confirming its well-known inhibitory and detrimental effect.14 All these cytokine abnormalities may
haematologica | 2021; 106(2)