The monoclonal antibody 265-1K1 reacts with human lactoferrin (LF), an 80 kDa glycoprotein. Lactoferrin was first isolated from human milk and plays an important part in the immune system and helps to fight infections. Lactoferrin promotes the health of the gastro-intestinal system by improving the intestinal microbial balance. In addition, LF can be found in epithelia and most body fluids and secretions.Lactoferrin is secreted in plasma by neutrophils. Its plasma concentration also represents a positive relation to the total pool of neutrophils and the rate of neutrophil turnover. In inflammation lactoferrin is released from secondary granules of neutrophilic leukocytes into the extracellular medium. Therefore the extracellular lactoferrin concentration can be used as an index for neutrophil activation.Lactoferrin strongly binds to iron and this iron binding property is considered to be an important antimicrobial. Human lactoferrin binds to bacterial products through its highly positively charged N-terminus, it kills various bacteria, most probably by inducing intracellular changes in these bacteria without affecting the membrane permeability. Cleavage by pepsin of lactoferrin leads to the release of lactoferricin H. This 47 amino acid peptide has more antimicrobial activity than its precursor and it can inhibit the classical but not the alternative complement pathway.Lactoferrin also plays a role in signal transduction, immunomodulation and has antiadhesive, anticancer, antiviral activity.