EPITOPE SPECIFICITY OF RABBIT IMMUNOGLOBULIN-G (IGG) ELICITED BY PNEUMOCOCCAL TYPE 23F SYNTHETIC OLIGOSACCHARIDE-PROTEIN AND NATIVE POLYSACCHARIDE-PROTEIN CONJUGATE VACCINES - COMPARISON WITH HUMAN ANTI-POLYSACCHARIDE 23F IGG
Ea. Develasco et al., EPITOPE SPECIFICITY OF RABBIT IMMUNOGLOBULIN-G (IGG) ELICITED BY PNEUMOCOCCAL TYPE 23F SYNTHETIC OLIGOSACCHARIDE-PROTEIN AND NATIVE POLYSACCHARIDE-PROTEIN CONJUGATE VACCINES - COMPARISON WITH HUMAN ANTI-POLYSACCHARIDE 23F IGG, Infection and immunity, 62(3), 1994, pp. 799-808
Streptococcus pneumoniae type 23F capsular polysaccharide (PS23F) cons
ists of a repeating glycerol-phosphorylated branched tetrasaccharide.
The immunogenicities of the following related antigens were investigat
ed: (i) a synthetic trisaccharide comprising the backbone of one repea
ting unit, (ii) a synthetic tetrasaccharide comprising the complete re
peating unit, and (iii) native PS23F (all three conjugated to keyhole
limpet hemocyanin [KLH]) and (iv) formalin-killed S. pneumoniae 23F. A
ll antigens except the trisaccharide-KLH conjugate induced relatively
high anti-PS23F antibody levels in rabbits. The epitope specificity of
such antibodies was then studied by means of an inhibition immunoassa
y. The cw(1-->2)-linked L-rhamnose branch was shown to be immunodomina
nt for immunoglobulin G (IgG) induced by tetrasaccharide-KLH, PS23F-KL
H, and killed S. pneumoniae 23F: in most sera L-rhamnose totally inhib
ited the binding of IgG to PS23F. Thus, there appears to be no major d
ifference in epitope specificity between IgG induced by tetrasaccharid
e-KLH and that induced by antigens containing the polymeric form of PS
23F. Human anti-PS23F IgG (either vaccine induced or naturally acquire
d) had a different epitope specificity: none of the inhibitors used, i
ncluding L-rhamnose and tetrasaccharide-KLH, exhibited substantial inh
ibition. These observations suggest that the epitope recognized by hum
an IgG on PS23F is larger than the epitope recognized by rabbit IgG. B
oth human and rabbit antisera efficiently opsonized type 23F pneumococ
ci, as measured in a phagocytosis assay using human polymorphonuclear
leukocytes.