Monoclonal antibody clone 1E4 recognizes mouse lactoferrin (LF). The expression of small proteins and peptides with microbial activity, also called antimicrobial peptides (AMPs), is considered to be a primitive mechanism of immunity. AMPs are produced by almost all cell types which are commonly exposed to microbes. Lactoferrin is a multifunctional AMP and a major element of innate immunity but also affects adaptive immune functions. LF is a well conserved mammalian non-haem iron-binding 80kD monomeric glycoprotein of the transferrin family. The protein is found in mucosal secretion like saliva, tears, urine, vaginal fluids, semen, urine and very high concentrations in (colostral) milk (1-7mg/ml). Its protective effects range from direct antimicrobial activities against a large panel of microorganisms, including bacteria, viruses, fungi and parasites, to anti-inflammatory and anticancer activities. The main functions of LF resided in specific domains and have predominantly be found in the N-terminal side. One of the main functions is inhibition of microbial growth by sequestration of iron, which is essential for growth. The N-terminal structure of LF is mainly responsible for this function. The N-terminal domain contains also a serine- protease-like activity which is involved in inactivation of host cell invasion by bacteria. Following infection, LF is released from secondary granules of neutrophils in blood and inflamed tissue and functions as pattern-recognition receptor. Therefore, LF plasma concentration represents a positive relation to the total pool of neutrophils and the rate of neutrophil turnover and can be used as an index for neutrophil activation. In the adaptive immune response, LF promotes the maturation of T-cell precursors into competent helper cells and by differentiation of immature B-cells into antigen presenting cells.