**Core Concept**
Multiple sclerosis (MS) is a chronic autoimmune disease characterized by demyelination of nerve fibers in the central nervous system (CNS). Treatment aims to reduce inflammation, slow disease progression, and manage symptoms.

**Why the Correct Answer is Right**
Interferon beta-1a (Avonex) is a recombinant form of the human protein interferon beta, which modulates the immune response and reduces disease activity in MS. It works by inhibiting the production of pro-inflammatory cytokines, such as tumor necrosis factor-alpha (TNF-alpha), and promoting the production of anti-inflammatory cytokines like interleukin-10 (IL-10). This leads to a reduction in inflammation and a decrease in the frequency and severity of MS relapses.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because while corticosteroids can reduce inflammation in MS, they are not a first-line treatment for chronic management and have limited efficacy in preventing relapses.
**Option B:** This option is incorrect because while glatiramer acetate (Copaxone) is a disease-modifying therapy for MS, it is not the correct answer in this case.
**Option C:** This option is incorrect because while natalizumab (Tysabri) is a highly effective treatment for MS, it is not the correct answer in this case.

**Clinical Pearl / High-Yield Fact**
Be aware that interferon beta-1a can cause flu-like symptoms, injection site reactions, and increased liver enzymes as common side effects. Regular monitoring of liver function tests is essential.

**Correct Answer: A. Interferon beta-1a (Avonex)**