Hemoglobin based oxygen carriers (HBOC) as blood substitutes are one of the great hopes of modern transfusion and emergency medicine. After the major safety-relevant challenges of the last decades seem to be largely overcome, current developments have in common that they are affected by degradation and excretion at an early stage in test organisms. Several possible mechanisms that may be responsible for this are discussed in the literature. One of them is CD163, the receptor of the complex of haptoglobin (Hp) and hemoglobin (Hb). The receptor has been shown in various studies to have an affinity for Hb in the absence of Hp. Thus, it seems reasonable that CD163 could possibly also bind Hb within HBOC and cause phagocytosis of the particles. In this work we investigated the role of CD163 for the uptake of our HbMP (hemoglobin sub-micron particles) in monocytes and additionally screened for alternative ways of particle recognition by monocytes. In our experiments, blockade of CD163 by specific monoclonal antibody proved to partly inhibit HbMP-uptake by monocytes. It appears however, that several other phagocytosis pathways for HbMP might exist, independent of CD163 and also Hb.

Soluble CD163 (sCD163) functions as a scavenger receptor for haptoglobin-hemoglobin complexes, and is mostly expressed by monocytes and macrophages. The level of soluble CD163 has been used to determine macrophage activation. Our goal was to determine whether the loading of M2 CD163 positive tumor-associated macrophages (TAMs) through the secretion of sCD163 affects overall survival in patients with DLBCL and eventually discriminates subgroups of patients with different prognosis. sCD163 levels were measured in 40 frozen serum samples from patients diagnosed with DLBCL and 30 healthy individuals (HI) using an enzyme-linked immunosorbent assay (ELISA). Statistical analyses were performed using SPSS version 28. The results showed that patients who achieved complete response after standard-of-care immuno-chemotherapy and were alive and disease-free after 12 months of follow-up, but had elevated sCD163 levels (above median) at diagnosis, presented a significantly worse overall survival compared to those with initial serum sCD163 levels below median (p=0.03). Consequently, serum sCD163 level in DLBCL patients may constitute a marker of long-term response to chemo-immunotherapy.