Immune subset-committed proliferating cells populate the human foetal intestine throughout the second trimester of gestation

The intestine represents the largest immune compartment in the human body, yet its development and organisation during human foetal development is largely unknown. Here we show the immune subset composition of this organ during development, by longitudinal spectral flow cytometry analysis of human foetal intestinal samples between 14 and 22 weeks of gestation. At 14 weeks, the foetal intestine is mainly populated by myeloid cells and three distinct CD3^-CD7⁺ ILC, followed by rapid appearance of adaptive CD4⁺, CD8⁺ T and B cell subsets. Imaging mass cytometry identifies lymphoid follicles from week 16 onwards in a villus-like structure covered by epithelium and confirms the presence of Ki-67⁺ cells in situ within all CD3^-CD7⁺ ILC, T, B and myeloid cell subsets. Foetal intestinal lymphoid subsets are capable of spontaneous proliferation in vitro. IL-7 mRNA is detected within both the lamina propria and the epithelium and IL-7 enhances proliferation of several subsets in vitro. Overall, these observations demonstrate the presence of immune subset-committed cells capable of local proliferation in the developing human foetal intestine, likely contributing to the development and growth of organized immune structures throughout most of the 2^nd trimester, which might influence microbial colonization upon birth.

Novel human MHC class I genes are expressed by tumour cell lines representing embryonic and extraembryonic tissues

The expression of HLA class I(-like) genes was studied in two human developmental tumour cell lines representing embryonic (Tera-2) and extraembryonic (Jeg-3) origins. Neither cell line expresses polymorphic HLA-A, -B, -C antigens as determined by standard serological typing. Tera-2 cells express the HLA class I-like T cell system A (TCA) determinants; Jeg-3 cells are TCA negative. Northern blot analysis using an HLA class I alpha 3 domain specific probe revealed markedly reduced levels of HLA class I(-like) transcripts in both cell lines, which can be upregulated in Tera-2 cells by incubation with gamma interferon (gamma IFN). Immunoprecipitation studies with a large panel of HLA class I/beta-2 microglobulin (beta 2m) monoclonal antibodies (mAbs), detect low quantities of regular HLA class I heavy chains that are not associated with beta 2m on the surface of Tera-2 cells. In contrast, Jeg-3 cells express significant amounts of cell membrane beta 2m associated molecules of 41 and 45 kilodalton (kD). Screening of a Tera-2 cDNA library, yielded 30 clones that hybridize to a full length HLA class I cDNA probe. Sixteen have been characterized and represent HLA class I sequences, consistent with the haplotype of Tera-2. A similar screening of a Jeg-3 cDNA library isolated clones representing a single novel HLA-C-like sequence; this probably codes for the 45 kD cell surface molecules of Jeg-3. The 41 kD molecule may be encoded by the HLA-6.0 gene since this is constitutively expressed in Jeg-3 cells.