Proteins from cow’s milk (CM), goat’s milk
(GM), GM cheese (GC), CM cheese (CC), total
goat caseins (GCN) and goat whey (GW) were
separated on 12% SDS-PAGE and blotted
onto membranes. Membrane were incubated
with the sera of two patients (#816 and
#820) and bound IgE revealed by a chemoluminescence method. M: molecular weight
marker.
No reactivity was found toward goat whey
proteins (lines GW) (the two bands at Mr
~65000 and ~70000 are artifacts, they
appear in every line even in case of totally
negative serum). These results are consistent
with previous observations (8). Patient 816
did not show any reactivity toward CM
proteins and patient #820 showed a very low
reactivity toward bovine αS-caseins and their
degraded forms in CM and cow’s cheese. It is
not possible to distinguish αS1- from αS2-casein but reactivity is most likely directed
against αS1-casein which is much more
abundant than αS2-casein. Surprisingly, both
patients recognized strongly bovine κ-casein
1-105 peptide from CM cheese whereas they
did not show any reactivity toward fulllength bovine κ-casein (compare Fig.1 “κ”
and Fig. 2). A similar reactivity was also
observed against κ-casein 1-105 peptide
from GM cheese. It is likely that the
intermediate reactivity of these patients
against CM cheese is mainly due to the strong
and specific recognition of this 1-105 κ-casein fragment which is generated during
cheese fabrication. The cleavage of κ-casein
by chymosin generates a strong
immunogenic peptide and an immune
reaction directed against an epitope which is
not recognized in the full-length protein.
Several hypothesis can be risen:1) the
epitope is not accessible in the full-length
protein; 2) a conformational epitope is
generated because peptide 1-105 adopts a
different conformation than full-length
protein; 3) the epitope includes the Cterminal amino acid residues of 1-105
peptide and it is recognized only when the
COOH of Phe105 is free (not included in
peptide bond). This is a very uncommon
situation in which proteolytic enzyme
cleavage is able to generate a new strong
immunogenic epitope