ES antigens are synthesized by Trichinella from different developmental
stages, and the source of ES antigens is the stichosome. The antigenicity
and composition of ES antigens of Trichinella vary according to the developmental
stage. The ES antigens of theML consist of a group of structurally
related glycoproteinswith molecularweights of 45–53 kDa [39].
Trichinella ML antigens have been classified into eight groups (TSL-1 to
TSL-8) based on their recognition by different monoclonal and polyclonal
antibodies. TSL-1 (45–100 kDa in the non-reduced form), TSL-2
(45 kDa in the non-reduced form), TSL-3 (45 kDa in the non-reduced
form), and TSL-5 (35 kDa in the non-reduced form) are present in ES
antigens of the ML. TSL-1 is the most abundant ES antigen [31]. A
immunocytolocalization study showed that the antibodies are distributed
in the hypertrophic nuclei and cytoplasm of parasitized nurse
cells and in the lumen of the larvae oesophagus and intestine tissues.
On the contrary, ES antigens of adult parasites are sometimes poorly
immunogenic and lack the specific 45–53 kDa antigens [31]. The NBL
cannot excrete/secrete any antigen; however, the NBL starts to form a
stichosome after invading muscle cells.