Cellular Differentiation of the Immune System of Mice

Abstract

Marrow cells and 5 x 107 thymocytes of unprimed (C57BL/6 x DBA/2)F1, (C57BL/10 x WB)F1 and (C3H x C57BL)F1 donor mice were mixed in vitro and transplanted into X-irradiated syngeneic hosts. Upon injection of sheep erythrocytes, splenic plaque-forming cells (PFC) secreting IgM (direct PFC or IgG (indirect PFC) hemolytic antibody were enumerated at the time of peak responses. By grading the numbers of marrow cells, inocula were found that contained few immunocompetent cells reaching the recipient spleens, interacting with thymocytes or other accessory cells (or both), and generating PFC. The frequency of responses in BDF1 mice conformed to Poisson statistics, indicating that immunocompetent marrow cells participated in a single-hit interaction limiting PFC responses. The marrow cells assayed were not restricted for the antibody class (IgM versus IgG) to be secreted by mature PFC. Unrestricted marrow cells could have been either the precursors of PFC or accessory cells. Different results were obtained in BWF1 and C3BF1 mice. The frequency of responses in relation to the number of marrow cells grafted did not follow Poisson statistics, and the limiting cells were restricted for antibody class. Presumably, immunocompetent cells of these strains were more heterogeneous than those of BDF1 mice and participated in a multiplicity of cell-to-cell interactions. The strain differences reflected inherent properties of marrow cells and not influences of the environment in which PFC were produced. The results confirmed for bone marrow the heterogeneity of immunocompetent cells reported by others for spleen, and suggested that genetic factors such as "immune response" genes regulate cellular differentiation also for functions other than those related to antibody specificity.

Antigen-Specific Cells in Mouse Bone Marrow

“…For one degree of freedom, the differences were statistically significant (P < 0.05). These results confirmed earlier experiments in which nonimmune C3BF1 marrow cells were grafted into fully syngeneic recipients, and PFC were enumerated by the original Jerne plaque assay in dishes (21,22). The non-Poisson distribution and the unequal frequencies of the two PFC responses suggested that potentially immunocompetent cells of C3BF1 marrow were class differentiated and heterogeneous for other properties as well.…”

“…It was of interest that immunization of marrow donors with the suboptimal number of 3.5 X 106 SRBC did not induce functional changes in precursor units of indirect PFC, while it did in precursor units of direct PFC. Dissociation of the two responses with regard to the shape of limiting dilution plots strengthened the interpretation of earlier experiments according to which marrow precursor units of PFC are restricted for the molecular class of antibody to be made by descendent PFC (21,22). Since limiting dilution plots for anti-CRBC responses conformed to the Poisson model regardless of whether marrow donors were immunized against SRBC or not, the present data cannot rule out the possibility that antigen-dependent differentiation or maturation of marrow cells was nonspecific, or affected cell types with functions not related to antibody specificity.…”

“…Conditions such as these were established by transplanting into several groups of irradiated mice 5 X 107 thymocytes with graded numbers of marrow cells. The distribution of anti-chicken PFC responses in the various treatment groups conformed to the expectations of the Poisson model, indicating that the assumptions made in designing the experiments (21,22) were presumably correct. The most important assumption concerned the existence in marrow of a cell type which alone limited the occurrence of an event essential for PFC formation.…”

“…The best known function of marrow-derived cells is the synthesis of antibody molecules (1-3, 6). Several lines of evidence suggest that cells with other accessory immune functions, yet to be defined, are also derived from bone marrow (5,6,21,22,25). Genetic information concerning molecular class of immunoglobulins is expressed differentially in marrow-derived cells (precursor or accessory cells) but not in thymic ARC (11,21,22).…”

“…In cell transfer systems, irradiated test animals can be provided with an excess of all required cell types, while limiting the availability of one (11,13,14,21,22,24). If an antibody response depends entirely on the presence or absence of the rarest cell type or functional unit of cells (all other cells or events being nonlimiting), the distribution of immune responses among mice given graded numbers of limiting cells will be dictated by Poisson statistics.…”