Seem to make up what are called "transfer factors"... which can be manufactured by beneficial/commensal species of microflora... glycoproteins are "complexed" proteins that seem to be used by microorganisms and living cells for communication with and between one another.
It seems that kefir is a good source of these, along with other various ferments... in addition, colostrum and then raw milk can be a good source as well.
"lactoferrin" has been referred to as lactotransferrin, which you may also want to read up on.
Note that I am of the opinion that pasteurization dramatically reduces or eliminates the glycoprotein content of dairy, HOWEVER, it is one of the things that fermentation with live probiotics can restore somewhat... just AVOID the homogenized dairy if you can.
looking up "glycoprotein" on a supplement vendor site will get you hits on most all products with medicinal mushrooms in them, lactoferrin supplements, and transfer factor products... among multivitamin and immune system boosting products that have these individual components as part of their formulations.