Lectins can do the following:
-cross the intact intestinal epithelium and appear in the bloodstream
and
thence distant organs.
-disrupt the brush border epithelium of the digestive mucosa allowing
themselves and other substances easier entry to the tissues and
bloodstream.
-kill T-cells- the officers of the immune system.(apoptosis)
-kill other cells
-make T-cells proliferate at the wrong time.(mitogenic effect)
-make other cells divide
-cause cells to present the wrong codes (HLA type 2 antigens) on their
surface, tricking the T-cells into thinking that an attack has been
made on
the body. This reaction causes the T-cells to target the body’s own
tissues,
triggering an autoimmune attack. I think (but not sure) that HLA type
2
antigens are normally used during infections by certain white blood
cells
(macrophages) to present bits of gobbled up germs to the T-lymphocytes
who
then launch the "smart tanks" (killer cells specific to that germs
antigens), and "smart bombs" (antibodies) etc. In due course, the
smart
tanks and smart bombs are tricked into attacking our tissues and
autoimmune
disease results, eg insulin dependent diabetes, rheumatoid arthritis.
-trick a cell into releasing a hormone eg insulin release
-trick a cell into thinking it was stimulated by a hormone again eg
insulin

Lectins can stimulate virtually any glycoprotein receptor on the
mammalian
cells. Many of these receptors have important jobs (eg being insulin
receptors etc.). Thus lectins are wonderfully devious- they
infiltrate, they
break down the defenses, kill or confuse the officers, send the troops
rampaging against the civilians, send false communications,. They make
James
Bond look like a bit of a patsy. All this, and still get home in time
or
tea.

See why I don't eat peas?

A good reference in a heavy book would be (chapter 4 I believe)(the
one
after Liener's chapter which is a bit dry) found in:
Shahidi, Fereidoon ed Antinutrients and Phytochemicals in Food 1997
Culinary
and Hospitality Industry Publications CHIPS (expensive- it's a
university
interlibrary loan type book). This is well written and you get the
picture
in a few pages cf Liener's 1980 Toxic Constituents of Plant Foodstuffs
which
is a good reference but nearly as exhausting as climbing a small
Himalayan
mountain.