*4.3.2.1. Transferrin*

Transferrin (Tf), the iron-binding protein of serum has been described as a negative acutephase protein. It is a strong chelator that is able to bind iron tightly but reversibly. The transferrin molecule has high affinity to bind two atoms of ferric iron (Fe3+), being higher in the extracellular pH of 7.4 and decreases in the acidified endosomes, allowing the dissociation of Fe3+ [192]. The primary role of transferrin is to transport iron safely around the body to supply growing cells [193]. Essentially, all iron circulating in the blood normally is bound to transferrin. It renders iron soluble under physiologic conditions, prevents iron-mediated free radical toxicity, and facilitates transport into cells [194]. Similar to lactoferrin, transferrin inhibits multiplication and growth of certain viral, bacterial, and fungal organisms by iron inhibition.

Moser et al. [195] evaluated the concentrations of transferrin in cattle in various physiological states, in energy-deficient (ketotic) cows, in cases of several acute and chronic infections, as well as after the administration of endotoxins. The values of transferrin in healthy animals ranged from 2.0 to 6.6 g/l. While in animals with acute infections and ketosis, the values were in the range of 1.5 and 8.5 g/l, chronic infectious diseases (such as paratuberculosis) were associated with relatively low values (below 2 g/l). The evaluation of the effect of age on transferrin concentrations showed its lower values in adult animals compared to young animals [195]. Tóthová et al. [122] presented a marked increase of transferrin concentrations from day 7 of life, reflecting acceptable rate of protein synthesis and good nutritional status. Furthermore, the concentrations of transferrin increased in veal calves with iron deficiency above 8 g/l, resulting in negative correlation between hemoglobin and transferrin [195].
