Surface layer proteins(SLPs)of lactic acid bacteria are primary proteins on the microbial surface,exhibiting diverse functionalities.This review provides an overview of the roles of SLPs in cell protection,inter-bacterial interactions,immune regulation,and nanotechnology.In-depth discussions are conducted on the applications of SLPs in supporting bacterial structures,regulating immune responses,and serving as nano-carriers and markers.The aim of this review is to offer new perspectives for future research on SLPs in microbiology,immunology,and nanotechnology.