Re: Why are the majority of white blood cells multi-nucleated?

Dear Afox,

Your question has a little error in it but I will try to assume, relative 
to your additional message that what you mean is nuclear morphology and 
not multi-nucleation. All peripheral blood white cells really only have 
one nucleus. Monocytes have one, relatively large nucleus that is bean 
shaped and can look like it has two lobes to its singular nucleus. 
Lymphocytes clearly have only one nucleus with a clock face pattern of 
dense chromatin. 

Now, the remaining peripheral blood white cells are the neutrophils, 
eosinophils and basophils. They also have only one nucleus with one set of 
chromosome pairs, but this nuceus is polymorphic in shape and can have up 
to five lobes connected with small narrow segments. Regardless of the 
number of bumps you see it is still only one nucleus.

This is why neutrophils, eosinophils and basophils are also called 
polymorphonuclear leukocytes.  Since all polymorphonuclear leukocytes are 
end-stage cells and do not go through additional cell division cycles 
after they enter the blood there isn't a great need to keep all the 
nuclear components ready for action. Maybe that is why they clump their 
DNA together into dense lobules like zipped computer files that you want 
to have around but don't use. The age of Polymorphonuclear leukocytes 
affects the number of the lobules in that the relatively recently produced 
cells might have a band shaped nucleus and very old cells may have more 
than 5 lobules to the nucleus. The function of polymorphonuclear 
leukocytes is very much oriented to their cytoplasm. These cells engulf 
bacteria and cell detritis, they digest what they eat and they also may 
release from granules certain factors (enzymes, cytokines and other 
molecules) that are manufactured in the cytoplasm. How they do this while 
most of their nuclear chromatin is clumped and not involved in 
transcription and translation is a puzzlement but maybe all of that was 
programmed while the cells were still in the bone marrow or while they 
still had a band shaped nucleus. Maybe you can do the research to answer 
that.

Both monocytes and lymphocytes undergo cell division at least once after 
leaving the bone marrow and during immune and inflammatory responses some 
of these cells may increase through multiple cycles of division. This is 
especially true for lymphocytes. Except during the period just before 
separation of dividing normal lymphocytes they virtually never show 
multiple nuclei. Monocytes, on the other hand, can form multiple nuclei 
under certain circumstances. During viral infection with measles virus or 
HIV virus monocytes fuse together to form a large cell with multiple 
nuclei. This is an abnormal formation related to the viral pathogenesis 
and is caused by the infecting virus. Monocytes also form multiple nuclei 
during certain kinds of inflammation or under certain kinds of 
stimulation. During infections with Mycobacterium tuberculosis, Listeria 
monocytogenes, Cryptococcus neoformans, and certain kinds of amebae, 
toxoplasma etc., mononuclear phagocytes that engulf these bacteria, fungi 
and parasites undergo division but do not divide. In which case, 
duplicates of their nuclei remain in one cell called a multinucleated 
giant cell. Such multinucleated giant cells form when mononuclear 
phagocytes ingest indigestible foreign bodies like plastic, wood 
splinters, or oils. We call these cells foreign body giant cells. 
Regardless of the inciting cause of foreign body cells their formation 
involves the cooperation of other cells that secrete cytokines. Cytokines 
are cell derived hormones that effect the function of leukocytes.

So, I hope this long aswer can help clarify your question.