Which of the following hypersensitivities are characterized by the slowest onset?ANSWERType IType IVType IIType III

Step 1: Break Down the Problem

To identify which type of hypersensitivity has the slowest onset, we need to understand the different types:

1. Type I: Immediate hypersensitivity (anaphylaxis, allergies).
2. Type II: Antibody-mediated cytotoxic hypersensitivity (e.g., hemolytic anemia).
3. Type III: Immune complex-mediated hypersensitivity (e.g., serum sickness).
4. Type IV: Delayed-type hypersensitivity (e.g., contact dermatitis).

Step 2: Relevant Concepts

• Onset of hypersensitivity reactions:
  • Type I reactions occur within minutes.
  • Type II and Type III reactions can occur within hours.
  • Type IV reactions typically manifest 24-48 hours after exposure.

Step 3: Analysis and Detail

• The key differentiator in the timing of the hypersensitivity reactions is the immune response involved.
• Type I hypersensitivity involves IgE antibodies and is known for rapid responses.
• Type II hypersensitivity involves IgG or IgM antibodies binding to antigens on cell surfaces.
• Type III hypersensitivity involves the formation of immune complexes that can take some time to trigger a response.
• Type IV hypersensitivity is primarily mediated by T-cells and does not involve antibodies, resulting in a delayed response.

Step 4: Verify and Summarize

Upon reviewing the characteristics of each type of hypersensitivity, it's evident that Type IV hypersensitivity has the slowest onset due to the nature of the T-cell mediated immune response.

Final Answer

Type IV hypersensitivity is characterized by the slowest onset among the options provided.