Taking an antigen into a cell and enzymatically cutting it into smaller pieces is known as what?

1. T cells do not recognise free-floating antigen, so antigen-presenting cells internalize it first. 2. Antigen processing is the mechanism that enzymatically cleaves the antigen into smaller pieces. 3. Antigen presentation is the later step, when a fragment sits in the peptide-binding cleft of an MHC molecule at the cell surface. 4. Processing therefore comes first and presentation second, so the two terms are not interchangeable. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 21 "The Lymphatic and Immune System", section 21.3 The Adaptive Immune Response: T lymphocytes and Their Functional Types_