Table 1.

The Ridley–Jopling classification of leprosy based on immune response¹⁸,²¹–²³

Immune response	High resistance		Unstable resistance		Little or no resistance
Clinical spectrum	Polar tuberculoid (TT)	Borderline tuberculoid (BT)	Borderline borderline (BB)	Borderline lepromatous (BL)	Lepromatous (LL subpolar and polar)
Number of skin lesions	Few, usually single	Few	Few or many	Many	Many
Bacillary load	0 or, rarely, 1+	1+	2+	3+	4+
Lepromin reaction	Positive	Positive	Positive, doubtful, or no response	Doubtful or no response	No response
Histology	Epithelioid granulomas ringed by numerous lymphocytes found around dermal appendages and nerves in both papillary and reticular dermis; extending up to the epidermis. Caseation necrosis may occur. Nerve edema, infiltration by acid-fast bacilli (AFB), or destruction.	Epithelioid granulomas with a moderate number of lymphocytes. Langhans giant cells can be present. Rare infiltration of subepidermal zone. Nerve edema, infiltration by AFB, or destruction.	Granulomas consist of foamy macrophages. Number of lymphocytes in granulomas is generally less but varies. Langhans cells absent. Dermal nerves show Schwann cell proliferation; infiltration by AFB, lymphocytes, and macrophages.	Increasing histiocytes and fewer epithelioid cells and lymphocytes. Foamy macrophages, lipid-laden granulomas with a Grenz zone (clear subepidermal zone) present. Globi (macrophages containing bacilli in large clumps) can be present but large globi are not. Nerve bundles damaged.	Massive granulomas or diffuse sheets of foamy lipid-laden granulomas with thin Grenz zone present. Multiple and even large multinucleate globi occur. Nerve bundles damaged.