Auto-Immunity

NCERT grounding

NCERT Class XII Biology, Chapter 7 (Human Health and Disease), Section 7.2.6, places auto-immunity inside the larger discussion of acquired immunity. The text is brief but every clause has been mined for PYQs. NCERT first reminds us that memory-based acquired immunity in higher vertebrates rests on the ability to distinguish foreign organisms (pathogens) from self-cells. It then notes two corollaries: higher vertebrates also distinguish foreign molecules, and — critically — that "sometimes, due to genetic and other unknown reasons, the body attacks self-cells", producing what NCERT calls auto-immune disease. NCERT explicitly names rheumatoid arthritis as a prevalent example and, in Section 7.2.7, lists auto-immune disease alongside allergy and organ-transplant rejection as the three abnormal contexts in which the immune system plays a central role.

"Sometimes, due to genetic and other unknown reasons, the body attacks self-cells. This results in damage to the body and is called auto-immune disease. Rheumatoid arthritis… is an auto-immune disease."

NCERT XII Biology, Section 7.2.6

NIOS Biology, Chapter 31 (Immunobiology — An Introduction), reinforces the same operating definition: the immune system identifies anything "foreign to itself" and acts to neutralize, eliminate or metabolize the foreign entity. Auto-immunity is therefore not a failure of strength but a failure of identification — the same effector machinery, pointed in the wrong direction. For NEET purposes, the entire NCERT passage above is in scope and is the textual seed for nearly every question we will see in the snapshot below.

Auto-immunity — mechanism and disease spectrum

Self/non-self discrimination — the property that fails

The vertebrate adaptive immune system carries roughly 10¹¹ T- and B-lymphocyte clones, each bearing a unique antigen receptor. During lymphocyte development, clones whose receptors bind strongly to self-antigens are deleted (central tolerance in thymus and bone marrow) or anergised in the periphery (peripheral tolerance). The surviving repertoire is, in principle, blind to self and reactive only to non-self. Auto-immunity is the breakdown of this filter: a self-reactive clone escapes deletion, is activated, expands, and directs antibodies or cytotoxic T-cells against the patient's own tissues.

NCERT keeps the cause deliberately vague — "genetic and other unknown reasons" — and NEET keys directly off that wording. The two best-validated triggers are HLA-linked genetic susceptibility (certain MHC alleles present self-peptides in a more inflammatory way) and molecular mimicry, in which a microbial epitope so closely resembles a self-epitope that a normal anti-pathogen response cross-reacts with host tissue. Both end in the same place: a self-antigen is treated as foreign.

The named NCERT example — rheumatoid arthritis

Rheumatoid arthritis (RA) is the only auto-immune disease that NCERT names in the chapter, which makes it the most testable. In RA, auto-antibodies (including rheumatoid factor and anti-citrullinated peptide antibodies) and self-reactive T-cells target the synovial membrane lining mobile joints. The synovium becomes inflamed, thickens into a pannus, and gradually erodes the underlying articular cartilage and bone. Joints — typically the small joints of the hands and feet, symmetrically — become swollen, stiff (worst in the morning) and progressively deformed. RA is the canonical NCERT auto-immune disease and the option-key for the 2022 statement-pair PYQ in our snapshot.

Myasthenia gravis — antibodies against acetylcholine receptors

Myasthenia gravis (MG) is a chronic auto-immune disorder in which auto-antibodies are produced against nicotinic acetylcholine receptors (AChR) on the post-synaptic membrane of the neuromuscular junction. Each motor nerve impulse releases acetylcholine into the synaptic cleft, but the antibodies block, cross-link and accelerate internalisation of the receptors. With fewer functional receptors, end-plate potentials fail to reach threshold, the muscle fibre fails to contract, and the patient experiences fatigability, drooping eyelids (ptosis), double vision and progressive weakness of skeletal muscle. NEET 2021 and 2022 both probed this disease as a one-mark MCQ — once asking for the disease name from the description, once trapping students by pairing it with the wrong descriptor.

Other auto-immune diseases NEET expects you to recognise

Beyond NCERT's two named diseases, NEET 2018 already tested four more in a single MCQ — psoriasis, rheumatoid arthritis, vitiligo and Alzheimer's — to check whether students can distinguish auto-immune from non-auto-immune pathology. The list below covers every auto-immune disease that has appeared in NEET MCQs or NCERT/NIOS supplementary text, organised by target tissue. Each card pairs the disease name with the self-antigen attacked — the exam-relevant unit of memory.

Treatment principle — dampen the immune response

Because the harmful agent in auto-immune disease is the patient's own immune system, no curative therapy yet exists. Management aims to suppress or modulate the misdirected response. Front-line drugs are corticosteroids (broad anti-inflammatory action), disease-modifying anti-rheumatic drugs such as methotrexate (cytotoxic to proliferating lymphocytes), and biologics that neutralise specific cytokines (anti-TNF-α in RA) or deplete B-cells (anti-CD20). For myasthenia gravis, acetylcholinesterase inhibitors are added to prolong the action of the remaining ACh at the NMJ, while immunosuppressants address the underlying antibody production. Type 1 diabetes is managed with exogenous insulin because β-cell loss is permanent.

Where auto-immunity sits among "abnormal" immune responses

NCERT lists three abnormal contexts in which the immune system plays a central role: allergies, auto-immune disease and organ-transplant rejection. NEET regularly tests whether students can distinguish them — every one of these has appeared as a one-mark MCQ. The differentiator is the target of the immune response and the direction of the malfunction: allergy is hyper-response to an external antigen, auto-immunity is response against self, immunodeficiency is loss of response, and graft rejection is a normal response directed at non-self transplanted tissue. The versus card below pins these distinctions side by side.

Worked examples

Common confusion & NEET traps