Rm. Hamadeh et al., ANTI-ALPHA-GALACTOSYL IMMUNOGLOBULIN-A (IGA), IGG, AND IGM IN HUMAN SECRETIONS, Clinical and diagnostic laboratory immunology, 2(2), 1995, pp. 125-131
Anti-alpha-galactosyl (anti-Gal) is a natural human serum antibody tha
t binds to the carbohydrate Gal alpha 1,3Gal beta 1,4GlcNAc-R (alpha-g
alactosyl epitope) and is synthesized by 1% of circulating B lymphocyt
es in response to immune stimulation by enteric bacteria, We were able
to purify secretory anti-Gal from human colostrum and bile by affinit
y chromatography on silica-linked Gal alpha 1,3Gal beta 1,4GlcNAc. We
found similar secretory anti-Gal antibodies in human milk, saliva, and
vaginal washings, Secretory anti-Gal from milk and saliva was exclusi
vely immunoglobulin A (IgA); that from colostrum and bile also contain
ed IgG and IgM isotypes. Serum was also found to contain anti-Gal IgM
and IgA in addition to the previously reported IgG, Anti-Gal IgA purif
ied from colostrum and bile had both IgA1 and IgA2, Secretory anti-Gal
from saliva, milk, colostrum, and bile agglutinated rabbit erythrocyt
es (RRBC) and bound to bovine thyroglobulin, both of which have abunda
nt alpha-galactosyl epitopes, The RRBC-hemagglutinating capacity of hu
man saliva, milk, bile, and serum was specifically adsorbed by immobil
ized Gal alpha 1,3Gal beta 1,4GlcNAc but not by Gal alpha 1;4Gal beta
1,4GlcNAc, Gal beta 1,3GalNAc, Gal beta 1,4GlcNAc, Gal beta 1,4GlcNAc
alpha 1,2Man, or Fuc alpha 1,2Gal beta 1,4GlcNAc. No RRBC-hemagglutina
ting activity could be detected in rat milk, rat bile, cow milk, or ra
bbit bile, suggesting a restricted species distribution for secretory
anti-Gal similar to that found for serum anti-Gal, Colostral anti-Gal
IgA bound strongly to a sample of gram-negative bacteria isolated from
the throats and stools of well children as well as to an Escherichia
coli K-l blood isolate. Colostral anti-Gal IgA inhibited the binding o
f a Neisseria meningitidis strain to human buccal epithelial cells, su
ggesting that this antibody may play a protective role at the mucosal
surface.