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Autoimmune diseases represent a complex group of disorders where the immune system erroneously attacks the body's own tissues. They can manifest in various ways, affecting nearly any part of the body, from the pancreas in Type 1 Diabetes to the myelin sheath of nerve fibers in Multiple Sclerosis. In essence, these diseases occur because the immune system cannot distinguish between self-antigens and foreign antigens.

Imagine a case of mistaken identity, where the body's defense mechanism fails to recognize its cells and attacks them as if they were harmful intruders. This can result in chronic inflammation, damage, and dysfunction of the affected tissues or organs. As there's no one-size-fits-all treatment, managing autoimmune diseases often requires an individualized approach aimed at reducing the immune response, controlling symptoms, and maintaining the body's ability to fight disease.

The immune system is like a specialized army within the body, tasked with identifying and neutralizing threats like infections. When functioning correctly, it discriminates between 'self' components, which belong to the body, and 'non-self' antigens, like pathogens. Antigens are essentially 'red flags' that signal the immune system to take action.

Diving deeper, the immune response is a multi-step process involving the recognition of antigens, activation of immune cells, and the coordination of a response that targets and neutralizes the invader. This response is usually precise, but in the case of molecular mimicry, it's like a spy disguising as a friendly force, leading to friendly fire. Understanding the underlying mechanisms of immune responses is pivotal for developing strategies to avert autoimmune attacks caused by molecular mimicry.

Antigens are the 'bulletin board' of cells, displaying molecular signals that the immune system uses to assess whether they are part of the body or external invaders. Structurally, antigens are usually proteins, peptides, or polysaccharides. Their specific sequences and shapes are what the immune system uses to recognize and remember pathogens.

In the context of molecular mimicry, a foreign antigen mimics a self-antigen closely enough that the immune system's detection mechanisms are fooled. This deceit can provoke an immune response against the body’s own cells, mistaking them for the pathogen that has similar molecular markers. The concept of antigens is foundational in immunology, and dissecting their role helps us to understand vaccine development, immune responses, and the intricacies of autoimmune conditions.