ABSTRACT
The qualities of antibody (Ab) responses provided by B lymphocytes and their plasma cell (PC) descendants are crucial facets of responses to vaccines and microbes. Metabolic processes and products regulate aspects of B cell proliferation and differentiation into germinal center (GC) and PC states as well as Ab diversification. However, there is little information about lymphoid cell-intrinsic functions of enzymes that mediate ether lipid biosynthesis, including a major class of membrane phospholipids. Imaging mass spectrometry (IMS) results had indicated that concentrations of a number of these phospholipids were substantially enhanced in GC compared to the background average in spleens. However, it was not clear if biosynthesis in B cells was a basis for this finding, or whether such cell-intrinsic biosynthesis contributes to B cell physiology or Ab responses. Ether lipid biosynthesis can involve the enzyme PexRAP, the product of the Dhrs7b gene. Using combinations of IMS and immunization experiments in mouse models with inducible Dhrs7b loss-of-function, we now show that B lineage-intrinsic expression of PexRAP promotes the magnitude and affinity maturation of a serological response. Moreover, the data revealed a Dhrs7b-dependent increase in ether phospholipids in primary follicles with a more prominent increase in GC. Mechanistically, PexRAP impacted B cell proliferation via enhanced survival associated with controlling levels of ROS and membrane peroxidation. These findings reveal a vital role of this peroxisomal enzyme in B cell homeostasis and the physiology of humoral immunity.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
Abbreviations used: Ag, antigen; Ab, antibody; WT, wildtype; KO, knockout; MZB, marginal zone B cell; FoB, follicular B cell; PC, plasma cell; Ig, immunoglobulin; GC, germinal center; ETC, electron transport chain; ROS, reactive oxygen species; mtROS, mitochondrial ROS; FAO, fatty acid oxidation; EL, ether lipid(s); 2D, 2-dimensional; MALDI, matrix-assisted laser desorption/ionization; IMS, imaging mass spectrometry; ER, Endoplasmic Reticulum; PexRAP, Peroxisomal Reductase Activating PPAR(; DHAP, dihydroxyacetonephosphate; G3P, glycerol-3-phosphate; CTV, CellTrace Violet; SRBC, sheep red blood corpuscule; TCR, T cell receptor; CD, Cluster of differentiation; AID, Activation-induced deaminase; GFP, Green fluorescent protein; NP-OVA, 3-Nitrophenylacetyl (NP)-ovalbumin (OVA); ASCs, Ab-secreting cells; CSR, class-switch recombination; MBC, memory B cell; NADPH, nicotinamide adenine dinucleotide phosphate; NAC, N-acetyl-L-cysteine; OCR, oxygen consumption rate; ECAR, extracellular acidification rate; RCDP, rhizomelic chondrodysplasia punctata; FAS, fatty acid synthase; Tmx, tamoxifen; 4OHT, 4-hydroxytamoxifen; PUFA, poly-unsaturated fatty acids; 2-DG, 2-deoxyglucose; FCCP, carbonyl cyanide 4-phenylhydrazone; BSA, bovine serum albumin; PSA, porcine serum albumin; H2DCFDA, dichlorodihydrofluorescein diacetate; ELISA, enzyme-linked immunosorbent assay; ELISpot, enzyme-linked immunosorbent spot; DHA, dihydroxyacetophenone; DAN, 1,5-diaminonaphthalene; timsTOF, trapped ion mobility spectrometry time-of-flight; SDS-PAGE, sodium dodecyl-sulfate polyacrylamide gel electrophoresis; SEM, standard error of means.
In my fatigue and haste to get this done, I uploaded a pdf file whose content did not match what it was said to be (in Supplemental materials), and duplicated what is to be in a cover letter to Journal Editors anyway. Also, I reconnected to my "referee self" and realized that the less different files Editors (and perhaps Referees) need to look at, the better, so the Supplemental Data and their Legends will be subsumed in other files.