Specific and nonspecific immunoregulatory events in the clonal response of human lymphocytes in vitro

Estimation of guinea pig antigen-specific and non-specific suppressor cell activity

A functional assay for the quantitative estimation of suppressor cell (SC) activity in guinea pigs has been developed. Cultures of antigen-stimulated peripheral blood lymphocytes (PBL) from sensitized guinea pigs develop SC activity. The suppression of proliferation can be demonstrated in antigen-stimulated autologous co-cultures of precultured and freshly isolated PBL. The extent of suppression is dependent on the preculture antigen concentration but not the preculture period and it consists, as demonstrated with PBL from doubly sensitized guinea pigs, of an antigen-specific and a non-specific component. The observed SC activities were not due to an alteration of the kinetics of the co-cultures. The estimates of suppression are highly dependent on corrections for the values of the control cultures. The present method may prove useful in immunological studies of mycobacterial infections in guinea pigs.

Secondary immunization with a protein antigen (tetanus toxoid) in man. Characterization of humoral and cell-mediated regulatory events

Tetanus toxoid (TET) was used as an immunogen to explore regulatory events occurring after secondary immunization in man. Changes in dose-response patterns, kinetics, and frequency of antigen-reactive cells in the peripheral blood, and the serum antibody titres were studied. The most striking feature of these studies was the finding that immediately after immunization, a brief period of decreased responsiveness preceded the expected amplification of antigen-specific humoral and cell-mediated responses. One day after immunization serum antibody levels declined to approximately half their initial values before the expected increase in titre. These results could not be explained by the formation of antigen-antibody complexes. Lymphoproliferative responses were also depressed 1 day after immunization but increased in both magnitude and sensitivity from 7 to 28 days after challenge. A decrease in thymidine incorporation evident at supraoptimal antigen concentrations also became progressively more prominent during this interval. Cell mixing experiments documented the presence of a radioresistant population present 1 day after immunization capable of suppressing TET-specific lymphoproliferative responses of autologous lymphocytes obtained before immunization. These suppressors are preferentially activated at high antigen concentrations. Limiting dilution analysis revealed a 30-fold increase in TET-reactive proliferating cells by 28 days after immunization. Expansion occurred first in cells recognizing high antigen concentrations and subsequently in cells recognizing lower doses. Taken together, these findings present a consistent if somewhat counterintuitive picture of some of the regulatory processes accompanying booster immunization. The earliest detectable event appears to be the application of an active suppressor mechanism, release from which signals initiation of those processes classically associated with an anamnestic response.

The reversal immune surveillance hypothesis: part II

The first part of the reversal immune surveillance hypothesis (RISH. I) describes the conceptual framework of the immune system as a homoeostatic mechanism for the control of cell differentiation and replication. The thymic dependent lymphocytes (T-cells) are considered to be tissue specific and identify aberrations in the cell surface pattern (antigens), that represent that particular cell type. The T-cells may then recruit antibody forming B-lymphocytes (B-cells) to produce antibodies (humoral response) to the cell surface antigens in order to return the cell surface pattern to its correct state. The antigens may also be removed from the cell surface as immune complexes by the complement system, which under normal conditions does not cause cell lysis. The cellular arm of the immune system, that of killer cells or activated macrophages are considered to be primarily involved with tissue remodelling. Whether or not the humoral or cellular arm of the immune system is activated depends upon the antigens displayed by the stimulating cell. The proposed system, which is self monitoring, is considered to have evolved from the invertebrates through to the vertebrates to become more complex in the mammals. Therefore the immune system is considered to be based on the identification of self and self-foreignness, rather than on foreignness per se.