Mechanisms of Generation of Antibody Diversity as a Cause for Natural Selection of Homoiothermal Animals in the Process of Evolution

Abstract

The temperature-dependence of domain interactions in the Fab, Fc, Fb and Fv fragments from human myeloma immunoglobulins (IgG) samples was investigated by scanning microcalorimetry, NMR and difference spectroscopy. The fragments were found to be very sensitive to temperature changes. Lowering the temperature below the physiological value (37 degrees C) considerably decreases the energy of interaction of the variable VH and VL domains, resulting at times in their dissociation. Since the association energies of VH and VL pairs can be affected by the result of somatic recombination and mutation events affecting antibody genes, immunoglobulins can fortuitously acquire the properties of cryoglobulins or cold autoantibodies and induce severe pathological states. It is postulated that this property of immunoglobulins, and by extension, of T-cell antigen receptors might have been one of the causes for the possible natural selection of homoiothermal animals. In these, the high conformational sensitivity of immunoglobulins to temperature change may be important in the mechanisms of induction of secondary functions in immune responses.

Three-Dimensional Structure of the Human Myeloma IgG2

“…At acidic pH values, all IgG and isolated Fc fragments studied exhibit a low-temperature peak of heat absorption, which corresponds to melting of the C H 2 domains [20]–[25]. Thermostability of C H 2 domains is lower than that of other domains because interactions in the pair of C H 2 domains are weaker in comparison with the pairs V L -V H , C L -C H 1 and C H 3- C H 3 domains [7], [26]–[28].…”

Influence of pH on Heat-Induced Aggregation and Degradation of Therapeutic Monoclonal Antibodies

“…19) Shimba et al reported that the CH1 and CL domains serve to improve the stability of the variable domains. 20) Ghirlando et al 21) and Mimura et al 22) reported that the CH2 domain of IgG1 and IgG4 is stabilized by the sugar moiety attached the domain.…”

“…25) It is quite important to compare antibodies having the 'same' variable regions (as used in this study) to analyze the effects of subtype on the stability of monoclonal antibodies because amino acid sequences of variable regions affect the stability of Fab. 19) Secondary Structure Analysis of Antibodies of Different Subclasses with the Same Variable Region Because different stabilities were observed by DSC analysis depending on the IgG subclasses, the secondary structures of the antibodies from the different subclasses were analyzed by CD spectroscopy. The CD spectra of three antibodies (G1-A, G2-A, G4-A) were nearly identical and characteristic of a bsheet structure (Fig.…”

Contribution of Variable Domains to the Stability of Humanized IgG1 Monoclonal Antibodies

“…Temperature-induced unfolding of human IgG1 and its Fab and Fc fragments was studied with the myeloma IgG1 Van by DSC in the pH range 3.5-5.5 and compared to the thermograms obtained from other human isotypes (IgG2, IgG3, and IgG4). 11 The unfolding of the human myeloma IgG1 at pH 5.5 presents two transitions with the melting temperatures (T m ) around 708C and 828C, and with the amplitude of the first peak much larger than that of the second peak. Studies on the Fab and Fc fragments of the same antibody reported a melting temperature of 708C for the Fab fragment 11 and melting temperatures of 668C and 828C for the Fc fragment.…”

“…11 The unfolding of the human myeloma IgG1 at pH 5.5 presents two transitions with the melting temperatures (T m ) around 708C and 828C, and with the amplitude of the first peak much larger than that of the second peak. Studies on the Fab and Fc fragments of the same antibody reported a melting temperature of 708C for the Fab fragment 11 and melting temperatures of 668C and 828C for the Fc fragment. 12 Based on these results one may infer that the first unfolding event in the intact human IgG1 antibody is associated with the melting of the CH2 domain in the Fc fragment and the melting of the Fab fragment, while the second transition represents mainly the unfolding of the CH3 domain.…”