Naked
DNA vaccination with the
TSH receptor (TSHR) does not, in most studies, induce TSHR
antibodies and never induces
hyperthyroidism in BALB/c mice.
Proteins expressed endogenously by vaccination are preferentially presented by major histocompatibility complex class I, but optimal T cell help for antibody production requires lysosomal processing and major histocompatibility complex class II presentation. To divert
protein expression to lysosomes, we constructed a plasmid with the TSHR ectodomain spliced between the
signal peptide and transmembrane-intracellular region of
lysosome-associated membrane protein (LAMP)-1, a
lysosome-associated membrane protein. BALB/c mice pretreated with
cardiotoxin were primed intramuscularly using this LAMP-TSHR chimera and boosted twice with
DNA encoding wild-type TSHR, TSHR A-subunit, or LAMP-TSHR. With each protocol, spleen cells responded to TSHR
antigen by secreting
interferon-gamma, and 60% or more mice had TSHR
antibodies detectable by ELISA. TSH binding inhibitory activity was present in seven, four, and two of 10 mice boosted with TSHR A-subunit, LAMP-TSHR, or wild-type TSHR, respectively. Importantly, six of 30 mice had elevated T4 levels and
goiter (5 of 6 with detectable
thyroid-stimulating antibodies). Injecting LAMP-TSHR intradermally without
cardiotoxin pretreatment induced TSHR
antibodies detectable by ELISA but not by TSH binding inhibitory activity, and none became
hyperthyroid. These findings are consistent with a role for
cardiotoxin-recruited macrophages in which (unlike in fibroblasts) LAMP-TSHR can be expressed intracellularly and on the cell surface. In conclusion, hijacking the TSHR to lysosomes enhances T cell responses and TSHR antibody generation and induces Graves'-like
hyperthyroidism in BALB/c mice by intramuscular naked
DNA vaccination.