The 2 antigen zones of the peritoneal cavity

The omentum protects the peritoneal cavity
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5812451/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2754314/

the peritoneal cavity contains the stomach, liver, large and small intestines, the kidneys, the gall bladder, pancreas, and the adrenal glands.

omentum stromal cells
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3481843/

there are two types of omentum cells involved in tissue repair as stromal cells
myeloid derived suppressor cells and MSC cells
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0038368

pericytes and myeloid derived suppressor cells
https://www.ncbi.nlm.nih.gov/pubmed/26296362

subgroup of myeloid derived suppressor cells : fibrocytes
https://www.ncbi.nlm.nih.gov/pubmed/26405600/
https://www.ncbi.nlm.nih.gov/pubmed/23757729

fibrocytes are potent stimulators of T cytotoxic cells
https://www.ncbi.nlm.nih.gov/pubmed/15767291

Based on our patten of inside and outside antigens is seems that the outer antigens would be collected by the B1 cells and processed by the MSC cells while the inner antigens would be taken up by the pericytes and shown to the myeloid derived stromal cells.