Immediate Hypersensitivity (Type 1 Hypersensitivity)

Epidemiology and Etiology:

• T_H2 type CD4+ T cells induce B cells to differentiate from naïve (surface IgM and IgD expressing) B cells to IgE-secreting B cells
• IgE antibody production
• Release of vasoactive amines and other mediators from mast cells
• Vascular dilation
• Edema
• Smooth muscle contraction
• Mucus production
• Recruitment of inflammatory cells
• inflammation

Common sites:

• Systemic:
• Anaphylaxis
• conjunctivitis
• Sinonasal
• Allergic rhinitis
• Hay fever
• bronchi
• asthma
• GI
• Allergic gastroenteritis

Gross features:

Histologic features:

• Immediate reaction
• vascular dilation
• edema
• mucus production
• late phase reaction (2-24h and onwards)
• eosinophils
• neutrophils
• basophils
• monocytes
• CD4+ T cells
• Tissue destruction (epithelial cell damage)

Immunophenotype:

Marker:

Sensitivity:

Specificity:

Molecular features:

Other features:

References:

• Robbins & Cotran Pathologic Basis of Disease (2005)