BACKGROUND: The peripheral immune system is implicated in modulating microglial 
activation, neurodegeneration and disease progression in amyotrophic lateral 
sclerosis (ALS). Specifically, there is reduced thymic function and regulatory T 
cell (Treg) number in ALS patients and mutant superoxide dismutase 1 (SOD1) 
mice, while passive transfer of Tregs ameliorates disease in mutant SOD1 mice. 
Here, we assessed the effects of augmenting endogenous CD4+ T cell number by 
stimulating the thymus using surgical castration on the phenotype of transgenic 
SOD1(G93A) mice.
METHOD: Male SOD1(G93A) mice were castrated or sham operated, and weight loss, 
disease onset and progression were examined. Thymus atrophy and blood CD4+, CD8+ 
and CD4+ FoxP3+ T cell numbers were determined by fluorescence activated cell 
sorting (FACS). Motor neuron counts, glial cell activation and androgen receptor 
(AR) expression in the spinal cord were investigated using immunohistochemistry 
and Western blotting. Differences between castrated and sham mice were analysed 
using an unpaired t test or one-way ANOVA.
RESULTS: Castration significantly increased thymus weight and total CD4+ T cell 
numbers in SOD1(G93A) mice, although Tregs levels were not affected. Despite 
this, disease onset and progression were similar in castrated and sham 
SOD1(G93A) mice. Castration did not affect motor neuron loss or astrocytic 
activation in spinal cords of SOD1(G93A) mice; however, microglial activation 
was reduced, specifically M1 microglia. We also show that AR is principally 
expressed in spinal motor neurons and progressively downregulated in spinal 
cords of SOD1(G93A) mice from disease onset which is further enhanced by 
castration.
CONCLUSIONS: These results demonstrate that increasing thymic function and CD4+ 
T cell number by castration confers no clinical benefit in mutant SOD1 mice, 
which may reflect an inability to stimulate neuroprotective Tregs. Nonetheless, 
castration decreases M1 microglial activation in the spinal cord without any 
clinical improvement and motor neuron rescue, in contrast to other approaches to 
suppress microglia in mutant SOD1 mice. Lastly, diminished AR expression in 
spinal motor neurons, which links to another motor neuron disorder, spinal 
bulbar muscular atrophy (SBMA), may contribute to ALS pathogenesis and suggests 
a common disease pathway in ALS and SBMA mediated by disruption of AR signalling 
in motor neurons.