Antigen/antibody concept
An antibody is a soluble immunoglobulin, whereas BCR is a surface immunoglobulin.
All types (peptide, polysaccharide, lipid, etc.) and forms (native, denatured, etc.) of antigens can be recognised by the BCR without the need for transformation, whereas only peptide antigens embedded in a Class I or Class II HLA molecule can be recognised by the TCR. On the other hand, the antigens recognised by the BCR are necessarily accessible, that is to say extra-cellular.
An antigen can also be recognised non-specifically by the immunoreceptors of innate immunity, the PRRs (Pattern Recognition Receptors) via danger patterns.
