Herpesvirus outbreaks are common in natural animal populations, but little is known about factors that favour herpesvirus infection and its consequences for the frigatebird nestlings.
We found that the plasma concentration of haptoglobin was strongly associated with the infection status and could predict probabilities of survival.
We also found that nestlings with clinical signs had lower baseline corticosterone concentrations and similar telomere length compared with healthy nestlings, whereas we did not find any association of the infection status with innate immune defenses or with nitric oxide concentration.
In this study, we examined the pathophysiological consequences of a disease probably attributable to herpesvirus infection for several markers of immune function, corticosterone, telomere length and inflammation.
In addition, we assessed whether any markers used in this study might be associated with the occurrence of visible clinical signs of the disease and its impact on short-term survival perspectives. To address our questions, in spring 2015, we collected blood samples from nestlings of the magnificent frigatebird (Fregata magnificens) that were free of any clinical signs or showed visible signs of the disease.
Overall, our results suggest that the plasma concentration of haptoglobin might be a valuable tool to assess survival probabilities of frigatebird nestlings facing a herpesvirus outbreak.
Haptoglobin (abbreviated as Hp) is the protein that in humans is encoded by the HP gene.[3][4] In blood plasma, haptoglobin binds free hemoglobin (Hb) released from erythrocytes with high affinity and thereby inhibits its oxidative activity. The haptoglobin-hemoglobin complex will then be removed by the reticuloendothelial system (mostly the spleen).
In clinical settings, the haptoglobulin assay is used to screen for and monitor intravascular hemolytic anemia. In intravascular hemolysis, free hemoglobin will be released into circulation and hence haptoglobin will bind the hemoglobin. This causes a decline in haptoglobin levels. Conversely, in extravascular hemolysis the reticuloendothelial system, especially splenic monocytes, phagocytose the erythrocytes and hemoglobin is relatively not released into circulation; however, excess hemolysis can release some hemoglobin causing haptoglobin levels to be decreased.
Mutations in this gene or its regulatory regions cause ahaptoglobinemia or hypohaptoglobinemia. This gene has also been linked to diabetic nephropathy,[8] the incidence of coronary artery disease in type 1 diabetes,[9] Crohn’s disease,[10]inflammatory disease behavior, primary sclerosing cholangitis, susceptibility to idiopathic Parkinson’s disease,[11] and a reduced incidence of Plasmodium falciparummalaria.[12]
Since the reticuloendothelial system will remove the haptoglobin-hemoglobin complex from the body, haptoglobin levels will be decreased in hemolytic anemias. In the process of binding hemoglobin, haptoglobin sequesters the iron within hemoglobin, preventing iron-utilizing bacteria from benefiting from hemolysis. It is theorized that, because of this, haptoglobin has evolved into an acute-phase protein. HP has a protective influence on the hemolytic kidney.[13][14]
Some studies associate certain haptoglobin phenotypes with the risk of developing schizophrenia.[15]