Structural analysis of effector functions related motifs, complement activation and hemagglutinating activities in Lama glama heavy chain antibodies

NATALIA SACCODOSSI; EMILIO DE SIMONE; JULIANA LEONI

VETERINARY IMMUNOLOGY AND IMMUNOPATHOLOGY

ELSEVIER SCIENCE BV

Año: 2012 vol. 145 p. 323 - 331

0165-2427

Abstract: Heavy chain antibodies (HCAbs), devoid of the light chains and the CH1 domain, are presentin the serum of camelids. IgG2 and IgG3 are HCAbs; whereas IgG1 has the conventional structure. The presence of conserved motifs related to effectos functions (Ci1q, FcRc, binding Prot A and G) and the complement activating and hemagglutinating activities of each isotype were evaluated in this study. Llamas (Lama glama) were immunized with sheep red blood cells (RBC) stroma and the different isotypes were purified from sera. Whole serum, IgM and IgG1 could activate complement; however, HCAbs (IgG2-IgG3) could not, despite the presence of the C1q binding motif in their primary sequence. Unlike IgM and IgG1, the fraction corresponding to IgG2-IgG3 did not display hemagglutinating activity. Our findings suggest that HCAbs can not crosslink efficiently with different antigens and that the C1q binding might be hindered by the proximity of the variable domains.