Health Desk
Sandeep Dhand
Nutritionist And Health Educator
Introduction
The human body is a wonderful creation, made up of millions of cells that work together to maintain health and protect against harm. Every day, our body faces attacks from bacteria, viruses, parasites, and other harmful agents. To fight these invaders, the body has a special defense system known as the immune system.
The immune system is like an army that guards the body. It identifies what belongs to the body (self) and what doesn’t (non-self). When foreign substances enter the body, the immune system recognizes them and starts a defense reaction to destroy or neutralize them. This process is called an immune response.
However, sometimes this powerful defense system can become unbalanced or confused. It may attack the body’s own tissues, fail to protect against infections, or react too strongly to harmless substances. These mistakes in immune function can lead to various diseases such as autoimmune disorders, allergies, or immunodeficiency conditions.
This article explains in simple words how the immune system works, the types of immune reactions, and their relation to human disease. It also discusses autoimmune diseases, HLA (Human Leukocyte Antigen) and its relation to disease, immunodeficiency disorders, and the future prospects of immunological research.
- The Immune System
What is the Immune System?
The immune system is the body’s defense mechanism against infection and disease. It is made up of cells, tissues, and organs that work together to recognize and destroy harmful invaders like bacteria, viruses, fungi, and parasites.
It has two main parts:
- Innate (Natural) Immunity
- Adaptive (Acquired) Immunity
1.1 Innate Immunity
Innate immunity is the first line of defense. It is present from birth and does not require previous exposure to a germ to act. It reacts quickly, often within minutes or hours, to any foreign invader.
Components of Innate Immunity:
Physical barriers: Skin and mucous membranes prevent entry of microbes.
Chemical barriers: Enzymes in saliva, tears, and stomach acid destroy microbes.
Cellular defenses: White blood cells like neutrophils, macrophages, and natural killer cells engulf and destroy germs.
Inflammation: A local response that causes redness, heat, and swelling to fight infection.
Innate immunity is non-specific. It reacts to a wide range of threats but does not remember them for future defense.
1.2 Adaptive Immunity
Adaptive immunity is more specific and powerful. It develops over time when the body is exposed to a particular germ or antigen. It also has a memory, which helps the immune system respond faster if the same invader attacks again.
Main Cells of Adaptive Immunity:
Lymphocytes: These are specialized white blood cells. There are two main types:
B cells: Produce antibodies that attack invaders in the blood.
T cells: Attack infected cells directly and help regulate the immune response.
Adaptive immunity is the basis for vaccination. When you are vaccinated, your immune system learns to recognize and remember the pathogen, so you are protected from future infections.
1.3 Organs of the Immune System
The immune system includes several organs and tissues:
Bone marrow: Produces blood cells, including immune cells.
Thymus: Matures T cells.
Spleen: Filters the blood and helps fight infections.
Lymph nodes: Trap invaders and provide a meeting place for immune cells.
Tonsils and adenoids: Protect against germs entering through the mouth and nose.
These organs work together like a network, ensuring that invaders are detected and destroyed quickly.
- Types of Immune Reactions and Their Relation to Human Disease
The immune system can react in different ways. Normally, it fights infections and heals the body. But sometimes, the reaction becomes abnormal or excessive, leading to disease.
2.1 Normal Immune Reaction
When a germ enters the body:
- The immune system recognizes it as foreign.
- It produces antibodies or activates immune cells to destroy it.
- After the invader is destroyed, the immune system returns to normal.
This balanced reaction keeps us healthy.
2.2 Abnormal Immune Reactions
When the immune system doesn’t work properly, it can cause diseases. Abnormal immune responses are of four main types, known as hypersensitivity reactions.
Type I: Immediate (Allergic) Reaction
Caused by allergens such as dust, pollen, food, or insect bites.
The immune system releases chemicals like histamine, causing itching, swelling, sneezing, or asthma.
Example: Asthma, allergic rhinitis, anaphylaxis.
Type II: Cytotoxic Reaction
The immune system mistakenly attacks body cells.
Example: Autoimmune hemolytic anemia, where red blood cells are destroyed by antibodies.
Type III: Immune Complex Reaction
Immune complexes (antigen-antibody combinations) deposit in tissues and cause inflammation.
Example: Rheumatoid arthritis, serum sickness.
Type IV: Delayed Type (Cell-Mediated) Reaction
Caused by T cells instead of antibodies.
Reaction takes 24–48 hours to develop.
Example: Tuberculosis skin test, contact dermatitis.
2.3 Relation to Human Diseases
Allergic Diseases: Overreaction to harmless substances.
Autoimmune Diseases: Immune system attacks its own body cells.
Immunodeficiency Diseases: Weak immune system that fails to fight infections.
Chronic Inflammatory Diseases: Long-term immune activation causing tissue damage.
Thus, both overactive and underactive immune responses can lead to disease.
- Autoimmune Diseases
3.1 What is Autoimmunity?
Autoimmunity means the body’s immune system mistakenly attacks its own tissues, thinking they are foreign. The body fails to recognize “self” and starts producing autoantibodies against its own cells.
Autoimmune diseases can affect almost any part of the body—joints, skin, kidneys, brain, or other organs.
3.2 Causes of Autoimmune Diseases
The exact cause is not always known, but possible factors include:
Genetic factors: Some families have a higher risk.
Infections: Some viruses may trigger autoimmunity.
Hormones: More common in women due to hormonal influence.
Environmental triggers: Stress, toxins, or drugs may start the process.
3.3 Common Autoimmune Diseases
- Rheumatoid Arthritis: The immune system attacks the joints, causing pain and swelling.
- Systemic Lupus Erythematosus (SLE): Affects multiple organs including skin, kidneys, and brain.
- Type 1 Diabetes: Destroys insulin-producing cells in the pancreas.
- Multiple Sclerosis: Damages the protective covering of nerves.
- Hashimoto’s Thyroiditis: The thyroid gland is attacked, leading to low thyroid levels.
- Graves’ Disease: Causes overactive thyroid due to antibody stimulation.
- Celiac Disease: Immune system reacts to gluten in the diet.
- Pernicious Anemia: Antibodies attack stomach cells that absorb vitamin B12.
3.4 Symptoms of Autoimmune Diseases
Although each disease affects different organs, common symptoms include:
Fatigue
Joint pain or swelling
Muscle weakness
Fever
Skin rashes
Digestive problems
These symptoms may come and go, making diagnosis difficult.
3.5 Treatment of Autoimmune Diseases
There is no permanent cure, but treatments aim to reduce symptoms and control immune response:
Corticosteroids (e.g., prednisone) to reduce inflammation.
Immunosuppressive drugs to slow immune activity.
Biological therapies targeting specific immune pathways.
Lifestyle support: Healthy diet, stress management, and rest.
The goal is to achieve balance—suppressing harmful immune reactions while maintaining protection against infections.
- HLA and Disease
4.1 What is HLA?
HLA stands for Human Leukocyte Antigen. It is a group of proteins found on the surface of most body cells. These proteins help the immune system recognize which cells belong to the body and which are foreign.
The genes that control HLA are located on chromosome 6, and they vary widely among individuals. This diversity helps protect the population from infections but also increases the risk of autoimmune diseases in some people.
4.2 Role of HLA in Immunity
HLA molecules present antigens (foreign or self) to immune cells.
They determine how strongly the immune system reacts to infections or vaccines.
They play a major role in organ transplantation—matching HLA types between donor and recipient helps prevent rejection.
4.3 HLA and Disease Association
Certain HLA types are linked to specific diseases:
Disease Associated HLA Type
Ankylosing Spondylitis HLA-B27
Type 1 Diabetes HLA-DR3, DR4
Rheumatoid Arthritis HLA-DR4
Celiac Disease HLA-DQ2, DQ8
Multiple Sclerosis HLA-DR2
Graves’ Disease HLA-DR3
This shows that genetics plays a major role in determining immune behavior.
- Immunodeficiency Disorders
5.1 What is Immunodeficiency?
Immunodeficiency means a weakened immune system that cannot defend the body properly against infections. It can be primary (congenital) or secondary (acquired).
5.2 Primary Immunodeficiency
These are inherited disorders present from birth.
Caused by defects in immune cells or proteins.
Examples include:
Severe Combined Immunodeficiency (SCID): Absence of both B and T cells.
Bruton’s Agammaglobulinemia: Lack of B cells and antibodies.
DiGeorge Syndrome: Defect in T-cell development.
Children with primary immunodeficiency often suffer from frequent, severe infections.
5.3 Secondary Immunodeficiency
Caused by external factors rather than inherited.
More common than primary types.
Causes include:
HIV/AIDS: Virus destroys CD4 T cells.
Malnutrition: Lack of proteins and vitamins weakens immunity.
Chemotherapy or radiation: Destroys bone marrow cells.
Chronic diseases: Diabetes, kidney failure.
Stress and aging: Natural immune decline.
5.4 Symptoms of Immunodeficiency
Frequent or severe infections
Slow wound healing
Recurrent pneumonia or sinus infections
Fatigue and weakness
Early detection and treatment can prevent complications.
5.5 Treatment
Antibiotics or antivirals to control infections
Immunoglobulin therapy to replace missing antibodies
Bone marrow transplant in severe cases
Nutritional support and healthy lifestyle to strengthen immunity
- Prospects in Immunology
6.1 Advances in Research
Modern science has made huge progress in understanding the immune system. Areas of advancement include:
Vaccines: New generation vaccines like mRNA (used for COVID-19).
Monoclonal antibodies: Used in cancer and autoimmune therapy.
Immunotherapy: Boosts the body’s immune system to fight cancer.
Gene therapy: Corrects genetic immune defects.
Stem cell research: Helps regenerate healthy immune cells.
6.2 Future Possibilities
Personalized immunology based on HLA typing.
Early prediction of autoimmune diseases.
Development of safer and more targeted treatments.
Artificial intelligence to study immune responses.
Nutrition-based immunity enhancement strategies.
- Conclusion
The immune system is a powerful defense mechanism that keeps us safe from infections and diseases. However, when it becomes overactive, underactive, or confused, it leads to various disorders such as allergies, autoimmune diseases, and immunodeficiencies.
Understanding immunological factors in disease helps doctors diagnose conditions better and design effective treatments. With ongoing research in genetics, molecular biology, and immunotherapy, the future of immune-related disease management looks very promising.
Taking care of our immunity through balanced nutrition, exercise, rest, stress control, and vaccination is the best way to maintain lifelong health.