Small molecules that must combine with large proteins to become immunogenic are called:
a. Complete antigens
b. Kinins
c. Antigenic determinants
d. Haptens

Verified step by step guidance

1. Understand the key terms in the question: 'immunogenic' means capable of inducing an immune response, and 'small molecules' refers to molecules that by themselves cannot trigger this response effectively.
2. Recall that 'complete antigens' are large molecules that can independently stimulate an immune response without needing to combine with other molecules.
3. Recognize that 'haptens' are small molecules that are not immunogenic on their own but can become immunogenic when they bind to larger carrier proteins.
4. Eliminate options that do not fit the description: 'kinins' are peptides involved in inflammation, and 'antigenic determinants' (epitopes) are specific parts of an antigen recognized by immune cells, not small molecules themselves.
5. Conclude that the correct term for small molecules that must combine with large proteins to become immunogenic is 'haptens'.

Key Concepts

Haptens

Haptens are small molecules that are not immunogenic by themselves but can elicit an immune response when attached to larger carrier proteins. They bind to antibodies or immune cells only after forming this complex, making them important in understanding immune recognition.

Complete Antigens

Complete antigens are molecules capable of inducing an immune response independently. They have both immunogenicity (ability to provoke immune response) and reactivity (ability to react with immune products), unlike haptens which require a carrier.

Antigenic Determinants (Epitopes)

Antigenic determinants, or epitopes, are specific parts of an antigen recognized by immune receptors like antibodies or T-cell receptors. They are the precise molecular structures that trigger immune recognition and response.