Healthy ways to strengthen your immune system according to the mainstream:

Don’t smoke.

Eat a diet high in fruits and vegetables.

Exercise regularly.

Maintain a healthy weight.

If you drink alcohol, drink only in moderation.

Get adequate sleep.

Take steps to avoid infection, such as washing your hands frequently and cooking meats thoroughly.

Compare this list to Natural Allopathic Medicines below. One look informs us that modern medicine is mentally crippled with ignorance.