Electrophoretically homogeneous antibody synthesized by spleen foci of irradiated repopulated mice.

10(6) splenocytes from primed donors were injected, together with sheep erythrocytes (SRBC), into X-irradiated syngeneic mice. 8 days later the spleens were excised and cut into small fragments, keeping track of their location in the organ. Each fragment was cultured individually for 24 hr in the presence of (14)C amino acids and the culture fluids were assayed for antibody activity. The antibody-producing fragments were found to be clustered in few restricted areas (foci) surrounded by negative tissue. The anti-SRBC antibody from single foci was purified by absorption on stroma followed by acid elution. Thereafter, it was subjected to electrophoresis and immunoelectrophoresis. The radioautography of the runs showed a considerable degree of homogeneity. Distinct and sharp spikes were localized in the beta and gamma region. The pattern of each focus is unique from the point of view of the number of spikes and their mobility. Eluates obtained from many pooled fragments gave a broad radioactive smear in beta-gamma region. Many foci synthesized antibody migrating as a single band. This homogeneous protein is probably the product of a clone of cells homogeneously differentiated. However, some foci producing two and probably more antibody bands were also encountered. Two interpretations of the finding can be given. Either more than one precursor may participate in the formation of a focus or a differentiation switch may occur during the clonal expansion.

Constancy of cross reactivity patterns during the anti-HL-A response.

Three immunizations yielding cross reacting anti-HL-A antibodies were followed for 1 year or more. The specificities of the antisera obtained at different times were determined from their reactivity against a selected cell panel. Each antiserum was titrated against cells presenting different degrees of cross reaction. An extensive absorption study of each antiserum, diluted to one cytotoxic unit, was also performed. The data obtained suggest that the cross reactivity pattern in each response is rather rigidly established from the beginning and that it has little chance to vary even after secondary stimulation from the same donor.

The homologues of rabbit b-allotypes on hare immunoglobulin light chains: an evolutionary puzzle.

Most alloantisera directed against the rabbit allotypes b4, b5, and b6 cross-reacted with hare IgG. The determinants recognized by antisera against the three allotypes were shown to reside on the same hare L chains. Hare immunoglobulins, when injected into b4, b5, or b9 rabbits, elicited the formation of antibodies which reacted with hare IgG and cross-reacted with those rabbit allotypes (except b9) absent from the recipient. The anti-b9 antisera tested lacked reactivity with hare IgG.

A homologue of the rabbit kappa-chain allotype b9 ON IgG from a cottontail rabbit.

Eight out of 12 anti-b9 antisera tested strongly bound 125IgG of only one of four individual cottontail rabbits (Sylvilagus floridanus). In addition to this apparent polymorphism of a b9 homologue in cottontail rabbits, a polymorphism defined by some anti-b5 antisera was found. Three of 15 anti-b5 antisera reacted with IgG from only two of the four cottontail rabbits. Reactions with anti-b4 and anti-b6 were similar to those with hare IgG. Most anti-b4 and anti-b6 antisera bound the IgG from each animal. The cottontails we tested also resembled the hare with respect to their weak reactivity with some anti-a2 antisera (Vh allotype) and strong reactivity with anti-15 (an allotype localized in the Fc portion of rabbit gamma-chains).

Long-term antibody synthesis in vitro. VI. Anti-allotype sera as probes of clonal products in affinity maturation.

A new experimental system is described for measuring the allotypic product of rabbit B cells during long-lasting in vitro antibody responses. The immunoenzymatic assays described allow determination of several parameters mapping in different regions of the same molecule, which can be measured and combined to yield a multidimensional picture of the time-course dynamics of antibody synthesis. The rabbit immune system responding to Escherichia coli beta-D-galactosidase was sample and disassembled by (a) culturing lymph node microfragments and (b) sorting out from among all anti-enzyme antibodies only those activating a mutant enzyme, AMEF, which bore the b4 or b9 allotype. A considerable simplification of the response was achieved in the microcultures as documented by cultures of heterozygous cells which produced only one allotype and by the fact that each culture showed a distinctive pattern when antibody titre, association constant, heterogeneity index, L-chain type, and k-chain allotype were considered together. This array of patterns was not an artifact but the result of disassembling a representative sample of the rabbit immune system into small components, since the b4/b9 ratio obtained by averaging the results of all cultures from a heterozygous rabbit lymph node was the same as the serum ratio. Despite the Poisson distribution of the responder microcultures, none of them was monoclonal; i.e. no antibodies homogeneous by all parameters tested were observed, This finidng supports the notion that in normal lymphoid tissue in its native tridimensional arrangement, one T cell can trigger several B cells clustered in one antibody-forming unit. This natural arrangement would ensure the monospecificity of the cluster (dictated by the T cell) while allowing for variation in affinity (depending upon the array of B cells in the unit). Accordingly our findings would results from the fact that as the size of the microfragments was reduced, the cells diluted out first were T cells, but as long as one of them was present, several B-cell clones were triggered. The b4/b9 pattern of any given culture remained constant over several months, but the ratio kappa/lambda underwent changes. An increase in molecules with non kappa-chains (which could not be reacted with anti-kappa-chain allotype antisera) was usually associated with a parallel decrease in antibody affinity. This occurred by the end of the antibody cycle and might be related to the regulation of antibody synthesis by T-cell suppressor factors.