A study of the contribution of mast cells to vaccination 
- Regulatory functions of Fcγ receptors  
 
Akademisk avhandling 
Som för avläggande av medicine doktorsexamen vid Sahlgrenska akademin  
vid Göteborgs universitet kommer att offentligen försvaras 
 i hörsal Arvid Carlsson, Medicinaregatan 3, Göteborg  
 
Tisday den 3 September 2013, kl 13:00 
av 
Yu Fang 
 
Fakultetsopponent 
Professor Birgitta Heyman 
Avd för medicinsk biokemi och mikrobiologi, Uppsala universitet, Uppsala 
Avhandlingen baseras på följande arbeten: 
I. Fang Y, Larsson L, Mattsson J, Lycke N & Xiang Z. Mast cells 
contribute to the mucosal adjuvant effect of CTA1-DD after IgG-
complex formation. J. Immunol. 2010; 185(5):2935-2941. 
II. Fang Y*, Zhang T*, Lidell L, Xu X, Lycke N & Xiang Z. The immune 
complex CTA1-DD/IgG adjuvant specifically targets connective tissue 
mast cells through FcγRIIIA and augments anti-HPV immunity after 
nasal immunization. Mucosal Immunol. 2013; doi: 10.1038/mi.2013.16. 
III. Fang Y*, Larsson L*, Bruhns P & Xiang Z. Apoptosis of mouse mast 
cells is reciprocally regulated by the IgG receptors FcγRIIB and 
FcγRIIIA. Allergy. 2012; 67(10):1233-1240. 
  
* Shared first authorship 
 
 
  
 
 
Göteborg 2013 
Abstract 
This thesis aimed to explore the regulatory roles of mast cells in vaccination. Mast cells have been 
increasingly recognized as important orchestrators of immune regulation in both health and disease, in 
addition to their classically defined roles in allergic diseases. One of the recently appreciated 
beneficial roles of mast cells is their involvement in augmenting the adjuvant effects that are critically 
important in successful vaccination.  
 
This study has focused on the interaction of mast cells with an adjuvant complex composed of IgG 
and CTA1-DD, a fusion protein consisting of the Al subunit of cholera toxin (CT) linked to a 
synthetic dimer of fragment-D of Staphylococcus aureus protein A (DD). As the DD domain 
unspecifically binds immunoglobulins, CTA1-DD and IgG form complexes potentially able to 
activate mast cells through Fcγ receptors. Indeed, CTA1-DD, in combination with polyclonal IgG, 
induced mast cell degranulation and the production of TNF-α, a cytokine important for the maturation 
and migration of antigen presenting cells, resulting in enhanced antigen-specific immune responses 
following immunization. 
 
Furthermore, only connective tissue mast cells (CTMCs), but not mucosal mast cells (MMCs), were 
found to be activated by CTA1-DD/IgG complexes. This effect was mediated by FcγRIIIA, an 
activating receptor that has been described to be only expressed on connective tissue mast cells. 
Indeed, FcγRIIIA-expressing connective tissue mast cells were found in the nasal submucosa. 
Responses to immunization facilitated by CTA1-DD/IgG were compromised in FcγRIIIA-deficient 
mice, and in mice pre-treated with a CTMC inhibitor.  
 
Interestingly, MMCs, which were present in mouse nasal mucosa, were not entirely bystanders in 
CTA1-DD/IgG-mediated adjuvanticity. We discovered that a balanced expression of FcγRIIB and 
FcγRIIIA was required for mast cells to resist apoptosis mediated by IgG immune complexes. 
Therefore, MMCs, which only expressed FcγRIIB, but not FcγRIIIA, underwent apoptosis as a result 
of treatment by CTA1-DD/IgG. MMCs were capable of phagocytosing ovalbumin (OVA), and 
engulfment of these MMCs by antigen presenting cells (APCs) could occur if the MMCs were 
induced to apoptose. Finally, the APCs were able to present OVA peptide to OVA-specific T cells. 
Thus, MMCs may also contribute to vaccination through cross-presentation.  
 
Safety is always a prioritized concern for developing adjuvants, especially when mast cells are 
involved. Remarkably, CTA1-DD did not function as a superantigen to activate mast cells which had 
captured IgE molecules with their FcεRI, indicating that CTA1-DD is safe for use in allergic patients in 
which mast cell FcεRI is occupied by antigen-specific IgE molecules. Furthermore, CTA1-DD/IgG 
immune complexes administered intranasally did not trigger systemic anaphylaxis. 
 
In conclusion, CTA1-DD/IgG may target both CTMCs and MMC through Fcγ receptors to enhance 
antigen-specific immune responses, probably through two distinct mechanisms. We propose that IgG 
immune complex-induced mast cell activation may be considered as a component of rationally 
designed mucosal adjuvants.  
 
Keywords: mast cell, vaccine, adjuvant, CTA1-DD, Fcγ receptor, apoptosis  
ISBN: 978-91-628-8721-6                                                   http://hdl.handle.net/2077/32946