The Primary Antibody Repertoire Represents a Linked Network of Degenerate Antigen Specificities

Abstract

In this study, germline Abs were used to select clones from a random dodecapeptide phage-display library. This revealed a much greater heterogeneity of binders than could be obtained with mutated daughter Abs that presumably had been selected in vivo by nominal Ag during active immune responses. We demonstrate that the pluripotency of germline Abs can subsequently be optimized by binding interactions that correlate with thermodynamic changes indicative of structural adaptations at the interface. This singular feature confers on each Ab a distinct window of Ag specificities, where the entropic space explored constitutes a thermodynamic signature of that particular Ab. Combining site plasticity may facilitate overlaps in such windows, with independent Abs converging onto common determinants with near identical binding affinities. In addition to providing for an amplified recognition potential, this networking of individual spectra of Ag specificities simultaneously facilitates the rapid recognition of Ag. Importantly, it also ensures that the primary response is composed of Abs with a high degree of “evolvability.”

Structural Elucidation of the Mechanistic Basis of Degeneracy in the Primary Humoral Response

“…Peptides were essentially derived using the Phage Display Peptide Library Kit (New England Biolabs, Cambridge, MA), as previously reported (6). Interactions between Ab and peptide and their thermodynamic analysis by surface plasmon resonance have also been previously reported (6).…”

“…It was suggested that a degree of polyreactivity within a germline Ab would provide a way by which a single Ab would be able to recognize a range of Ags and so obviate the requirement for a singular Ab for every potential non-self immunogen (5)(6)(7)(8)(9). Even the mutation-driven modulations of epitopes could be handled very efficiently by primary humoral immune defense through use of such polyreactive Abs (10).…”

“…Its mature counterpart Bg 53-5 contains 11 point mutations, 1 in the L chain and the remaining 10 in the H chain (13). Through extensive kinetic and thermodynamic analyses, BBE6.12H3 was shown to bind to a series of independent dodecapeptide Ags (5,6). In the current study, four among those peptide Ags-namely, B6-13, 3, BA7-09, and B6-07, which bind to the germline mAb BBE6.12H3 with K d values of 0.38 mM, 0.80 mM, 0.60 mM, and 0.26 mM, respectively (6)-were subjected to crystallographic analysis.…”

Diversification post-traductionnelle de la spécificité des immunoglobulines

“…Cependant, la diversité dérivant uniquement de ces mécanismes est limitée et ne permet pas de faire face à l'hétérogénéité, théoriquement infinie, des antigènes potentiels présents dans la nature ou générés de manière synthé-tique. Cette limitation est compensée par la dégénérescence de la spécificité de certains récepteurs immunitaires, qui peut être considérée comme un deuxième niveau de diversification du réper-toire immunitaire [3,4]. Ainsi, certaines immunoglobulines (Ig) membranaires et solubles sont capables de s'adapter à de nombreux antigènes structurellement différents.…”

“…Ces immunoglobulines sont dites polyréactives [4]. Un grand nombre de travaux suggèrent que la capacité des anticorps polyréactifs à se lier à de multiples déterminants antigéniques est due à la plasticité conformationnelle de leurs domaines de liaison à l'antigène, qui leur permet de s'adapter à de nombreuses structures et séquences antigéniques différentes [3,4]. Dès lors, un répertoire normal d'immunoglobulines possède un continuum de réactivités antigéniques, allant d'une spécificité antigénique très restreinte (monoréac-tivité), à la capacité de reconnaître des antigènes structurellement différents (polyréactivité) [4].…”