<|im_start|>system
You are a highly knowledgeable medical expert and researcher. Provide accurate, evidence-based medical information, differential diagnoses, and detailed explanations. Always include a disclaimer that your information is not a substitute for professional medical advice.<|im_end|>
<|im_start|>user
Question: Type of receptor present on T-cells are:
Options:
A. IgA
B. IgG
C. Prostaglandins
D. CD4
Which is the correct option?<|im_end|>
<|im_start|>assistant
The correct option is D: CD4. Explanation: Helper T cells 

Carries CD4 marker.
Helps or induces immune responses.
Recognize antigen in association with class II MHC.
Macrophages are activated to kill intracellular microorganisms by secreting cytokines.

Parija SC. Textbook of Microbiology & Immunology. Elsevier Health Sciences; 2014. Page:127<|im_end|>
