Thiopalmitoylation of Myelin Proteolipid Protein Epitopes Enhances Immunogenicity and Encephalitogenicity

Abstract

Proteolipid protein (PLP) is the most abundant protein of CNS myelin, and is posttranslationally acylated by covalent attachment of long chain fatty acids to cysteine residues via a thioester linkage. Two of the acylation sites are within epitopes of PLP that are encephalitogenic in SJL/J mice (PLP104–117 and PLP139–151) and against which increased immune responses have been detected in some multiple sclerosis patients. It is known that attachment of certain types of lipid side chains to peptides can result in their enhanced immunogenicity. The aim of this study was to determine whether thioacylated PLP peptides, as occur in the native protein, are more immunogenic than their nonacylated counterparts, and whether thioacylation influences the development of autoreactivity and experimental autoimmune encephalomyelitis. The results show that in comparison with nonacylated peptides, thioacylated PLP lipopeptides can induce greater T cell and Ab responses to both the acylated and nonacylated peptides. They also enhanced the development and chronicity of experimental autoimmune encephalomyelitis. Synthetic peptides in which the fatty acid was attached via an amide linkage at the N terminus were not encephalitogenic, and they induced greater proportions of CD8+ cells in initial in vitro stimulation. Therefore, the lability and the site of the linkage between the peptide and fatty acid may be important for induction of encephalitogenic CD4+ T cells. These results suggest that immune responses induced by endogenous thioacylated lipopeptides may contribute to the immunopathogenesis of chronic experimental demyelinating diseases and multiple sclerosis.

Mechanism of modulation of T cell responses by N‐palmitoylated peptides

“…Several reports have indicated that N-palmitoylation of antigenic peptides can reduce T cell-dependent responses in vivo [15][16][17][18]. We show here for the first time that the mechanistic base for such an effect at the T cell clonal level is that N-palmitoylation weakens the agonist properties of the wild-type peptide.…”

“…However, the N-palmitoylated version of such peptides inhibit the subsequent response not only to the native peptide (Fig. 6) but also to the thioacylated peptide [17]. The fact that PALPCC 81-104 failed to prime could be explained by virtue of being a weak agonist, but we cannot rule out the possibility that PALPCC 81-104 peptide may also induce anergy to itself.…”

“…For example, it has been previously shown that the type of linkage between the peptide and the palmitic acid can affect the immunogenicity and encephalogenicity of the modified peptide in vivo [17]. While Npalmitoylation of encephalitogenic peptides can prevent the induction and reduce the clinical and pathological manifestations of EAE [15][16][17], thiopalmitoylation does not protect but in fact, increases immunogenicity [17,28,29].…”

“…Since previous in vivo studies in EAE implied that Npalmitoylation of antigenic peptides converted them into effective tolerogens [15][16][17], we decided to study their mechanism of action. We used the response to PCC , and tested the effect of N-palmitoylation of PCC to modify the response of a PCC 81-104 -specific T cell clone.…”

“…We chose Npalmitoylation because previous work has shown a therapeutic effect of N-palmitoylated peptides on experimental autoimmune encephalomyelitis (EAE). This work involved three peptides (PALPLP [139][140][141][142][143][144][145][146][147][148][149][150][151] , Npalmitoylated myelin basic protein (MBP) fragment 68-86, and N-palmitoylated myelin oligodendrocyte glycoprotein (MOG) fragment 35-55), in two species (mouse and rat), and with three different restriction elements ( [15][16][17][18] and GHS, personal observation). Using PCC and its N-palmitoylated version PALPCC we show that this modification converts a strong agonist peptide into a weak agonist of the TCR as indicated by the signaling pattern through this receptor and by the responses induced by PALPCC .…”