The yellowish milk produced by the mother during the initial few days of lactation is called colostrum.
It contains immunoglobulin A (IgA) which is essential to the new born baby to develop immunity.
Natural killers, macrophages and monocytes are not in colostrum, they are a kind of phagocytic cells and play an essential role as cellular barriers in innate immunity.
Monocytes : These are a type of WBCs and play an important role in destroying the invaders (pathogens) in the body. They are found in the blood and when required differentiate into macrophages.
Macrophages: These have the ability to move across the walls of the blood vessels and reach tissues. They help in destroying pathogens such as bacteria by phagocytosis and help in the release of cytokines as part of the immune response.
Natural Killer Cells: These stop the spread of infections by destroying the infected host cells.