Deficiency of the Intramembrane Protease SPPL2a Alters Antimycobacterial Cytokine Responses of Dendritic Cells

J Immunol. 2021 Jan 1;206(1):164-180. doi: 10.4049/jimmunol.2000151. Epub 2020 Nov 25.


Signal peptide peptidase-like 2a (SPPL2a) is an aspartyl intramembrane protease essential for degradation of the invariant chain CD74. In humans, absence of SPPL2a leads to Mendelian susceptibility to mycobacterial disease, which is attributed to a loss of the dendritic cell (DC) subset conventional DC2. In this study, we confirm depletion of conventional DC2 in lymphatic tissues of SPPL2a-/- mice and demonstrate dependence on CD74 using SPPL2a-/- CD74-/- mice. Upon contact with mycobacteria, SPPL2a-/- bone marrow-derived DCs show enhanced secretion of IL-1β, whereas production of IL-10 and IFN-β is reduced. These effects correlated with modulated responses upon selective stimulation of the pattern recognition receptors TLR4 and Dectin-1. In SPPL2a-/- bone marrow-derived DCs, Dectin-1 is redistributed to endosomal compartments. Thus, SPPL2a deficiency alters pattern recognition receptor pathways in a CD74-dependent way, shifting the balance from anti- to proinflammatory cytokines in antimycobacterial responses. We propose that in addition to the DC reduction, this altered DC functionality contributes to Mendelian susceptibility to mycobacterial disease upon SPPL2a deficiency.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antigens, Differentiation, B-Lymphocyte / genetics
  • Aspartic Acid Endopeptidases / genetics
  • Aspartic Acid Endopeptidases / metabolism*
  • Cattle
  • Cell Membrane / metabolism*
  • Cells, Cultured
  • Cytokines / metabolism
  • Dendritic Cells / immunology*
  • Genetic Predisposition to Disease
  • Histocompatibility Antigens Class II / genetics
  • Humans
  • Immunity
  • Immunomodulation
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism*
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Mycobacterium bovis / physiology*
  • Toll-Like Receptor 4 / immunology
  • Tuberculosis, Bovine


  • Antigens, Differentiation, B-Lymphocyte
  • Cytokines
  • Histocompatibility Antigens Class II
  • Membrane Proteins
  • Tlr4 protein, mouse
  • Toll-Like Receptor 4
  • invariant chain
  • Aspartic Acid Endopeptidases
  • SPPL2a protein, mouse