Jean, I'll take a stab at answering your question

>Is my information outdated? I seem to remember hearing that the
>lactoferrin is supposed to attack the cell wall of bacteria to remove
>iron for the baby's absorption (and kill the bacteria in the process).

The major protective function of lactoferrin is always ascribed to its iron
binding capacity. However it is really much more complex than just this one
action .  
Lactoferrin has a low iron saturation in human milk (<10%). In this form it
has bacteriostatic properties due to its high affinity for binding free iron
and thus depriving micro organisms of the iron they require to grow and
replicate.

It also inhibits bacterial growth by interaction with the bacterial membrane
of bacteria. These interactions alter the permeability and membrane function
of the microorganisms.

Also when lactoferrin is cleaved ("breaks up") in the presence of gastric
pepsin, a bactericidal peptide called lactoferricin is released - this has
potent broad spectrum bacteriacidal properties.

Lactoferrin both in iron saturated and iron unsaturated form activates
natural killer cells.

Lactoferrin also inhibits adhesion and impairs invasiveness of bacteria and
may have significant anti infective properties against enteropathogens
because of this. 

Interestingly several enteric bacteria such as strep faecalis and
Bifidobacteria are highly resistant to lactoferrin, indeed lactoferrin is
thought to stimulate the growth of Bifidobacteria  (Interestingly though
bovine lactoferrin in infant formula does not result in the high level of
bifidobacteria common in breastfed infants - as we all know!)

Lactoferrin also has many other actions including anti inflammatory effects,
as a growth factor and of course facilitating iron absorption

So, will concurrent administration of breastmilk and formula interfere with
any of these activities?

Oral iron therapy for the infant is thought to interfere with the
bacteriostatic action of lactoferrin by reducing its unsaturated state. Iron
containing formula would conceivably do the same thing.

Also the bacteriocidal actions altering the permeability and membrane
function of bacteria are reversed by iron saturation of lactoferrin which
may also occur in the presence of formula.

Lactoferrin also functions in synergy with IgA - perhaps this synergy may be
disrupted in the presence of formula

Lactoferrin is so complex and there is still so much to discover about its
roles both as an anti inflammatory and in fighting infection that it is
probably not possible to say how these myriad of functions might be affected
when the normal breastmilk environment is diluted out with formula or
whether effects occur because of direct mixing in the gut or bottle or
simply because the intestinal environment has been changed due to the
presence of formula.

Personally I never can bring myself to mix it prior to giving by tube or
bottle and I always give the breastmilk first. Whether waiting or perhaps
alternating breastmilk feeds with formula would make a difference I don¹t
know. Perhaps some of the impairment of lactoferrin function will occur
anyway  because of the change in gut flora and environment.

References for anyone interested in lactoferrin in milk

Hamosh, Margaret. 1998. Protective Function of proteins and lipids in human
milk. Biology of the Neonate. 74: 163-176.

Lonnerdal & Iyer. 1995. Lactoferrin: Molecular structure and biological
function. Annual Rev Nutr. 15: 93-110.

Sorry its so long

Cathy Fetherston
Perth Western Australia

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