Parenteral adjuvant potential of recombinant B subunit of Escherichia coli heat-labile enterotoxin

Abstract

BACKGROUNDThe B subunit of Escherichia coli heat-labile enterotoxin (LTB) is a potent mucosal immune adjuvant. However, there is little information about LTB's potential as a parenteral adjuvant.OBJECTIVESWe aimed at evaluating and better understanding rLTB's potential as a parenteral adjuvant using the fused R1 repeat of Mycoplasma hyopneumoniae P97 adhesin as an antigen to characterise the humoral immune response induced by this construct and comparing it to that generated when aluminium hydroxide is used as adjuvant instead.METHODSBALB/c mice were immunised intraperitoneally with either rLTBR1 or recombinant R1 adsorbed onto aluminium hydroxide. The levels of systemic anti-rR1 antibodies (total Ig, IgG1, IgG2a, and IgA) were assessed by enzyme-linked immunosorbent assay (ELISA). The ratio of IgG1 and IgG2a was used to characterise a Th1, Th2, or mixed Th1/Th2 immune response.FINDINGSWestern blot confirmed rR1, either alone or fused to LTB, remained antigenic; anti-cholera toxin ELISA confirmed that LTB retained its activity when expressed in a heterologous system. Mice immunised with the rLTBR1 fusion protein produced approximately twice as much anti-rR1 immunoglobulins as mice vaccinated with rR1 adsorbed onto aluminium hydroxide. Animals vaccinated with either rLTBR1 or rR1 adsorbed onto aluminium hydroxide presented a mixed Th1/Th2 immune response. We speculate this might be a result of rR1 immune modulation rather than adjuvant modulation. Mice immunised with rLTBR1 produced approximately 1.5-fold more serum IgA than animals immunised with rR1 and aluminium hydroxide.MAIN CONCLUSIONSThe results suggest that rLTB is a more powerful parenteral adjuvant than aluminium hydroxide when administered intraperitoneally as it induced higher antibody titres. Therefore, we recommend that rLTB be considered an alternative adjuvant, even if different administration routes are employed.

The Potential Adjuvanticity of CAvant®SOE for Foot-and-Mouth Disease Vaccine

“…The production of IgG1 isotype is generally reflected Th2 cytokines which promote humoral immune responses, whereas IgG2a isotypes indicate the involvement of Th1-type cytokines which promote the generation of cellular immune responses. The ratio of these two isotypes indicates the type of immune response generated against a given antigen [44,45]. We, therefore, examined the ratios of IgG2a to IgG1 antibody generated in response to vaccination, iA22-CAvant ® SOE vaccination groups show mixed Th1/Th2 immune responses, indicating that CAvant ® SOE adjuvant-induced higher and balanced humoral and cellular immune responses.…”

SARS-COV-2 RBD Oral Vaccine Boosted by Mucosal Immune Adjuvant LTB26 via DCs and B Cells Activation in Mice

“…However, the toxicity of LT prevented its application in human. In recent years, non-toxic LTB adjuvant had been widely studied 6,9,24,25,26 .…”

“…However, the toxicity of LT prevented its application as adjuvant in human. In recent years, non-toxic LTB adjuvant had been widely used(Cunha, Moreira et al, 2017, Ghazali-Bina et al, 2019, Holmner et al, 2011, Liu, Ma et al, 2016, Ma, Luo et al, 2012). The binding specificity of LTB to GM1 was associated with adjuvant activity.…”