““The way immunity works is that one's immune system initially learns about a new pathogen when antigen presenting cells (APCs) carry an antigen (fragment of a pathogen) back to your B memory cells, which live in your lymph system. The APC also tells you B cell where it found the antigen. An antigen could be a spike protein, or some other protein in/on the virus, or it could be something else like an oligosaccharide. Each B cell that receives an APC with a payload will try to construct an antigen-specific immunoglobulin (antibody) that should match that antigen fragment. Those antibodies will have two prongs that can grab the pathogen by that fragment, and they will have one opposing prong that will bind to any of several passing immune cells, such as T cells, which will destroy the antibody and its payload.”

The initial claim that APCs carry antigens back to B memory cells in the lymph system is inaccurate. APCs such as dendritic cells, macrophages, and B cells themselves present processed antigen fragments primarily to T cells, especially helper T cells (CD4+), not directly to B memory cells. APCs do not 'tell' B cells where they found the antigen; rather, B cells recognize native antigen via their B cell receptors (BCRs) and can act as APCs themselves to T cells.cwoer.ccbcmd.educwoer.ccbcmd.eduThe Adaptive Immune System: Antigen-Presenting Cells (APCs)library.fiveable.melibrary.fiveable.meAntigen-Presenting Cells (APCs) - (Anatomy and Physiology I)+2 more

Antigens can indeed be proteins like spike proteins or other molecular structures such as oligosaccharides; this part is correct.

The description that each B cell tries to construct an antigen-specific immunoglobulin (antibody) upon receiving an APC with a payload is misleading. B cells have pre-existing BCRs generated by gene rearrangement; they do not 'construct' antibodies de novo upon antigen presentation. Instead, when a B cell's receptor binds its specific antigen, it internalizes it and presents fragments on MHC II molecules to helper T cells for activation and differentiation into plasma cells producing antibodies.

The statement about antibodies having 'two prongs that can grab the pathogen by that fragment' is a simplified but roughly accurate description of the bivalent antigen-binding sites of antibodies.

The claim that antibodies have 'one opposing prong that will bind to any of several passing immune cells, such as T cells, which will destroy the antibody and its payload' is incorrect. Antibodies have an Fc region that can bind Fc receptors on various immune effector cells (e.g., macrophages, NK cells), facilitating pathogen clearance via opsonization or antibody-dependent cellular cytotoxicity. However, T cells do not typically bind antibodies to destroy them; rather, cytotoxic T cells recognize infected cells presenting antigen via MHC I. Antibodies themselves are not destroyed by T cells in this manner.